Truth is unless pakistan gets 5th gen aircraft its mostly checkmate.Ultimately money talks and you get what you pay for.
S-400 can neutralize conventional fighters(unless flying ground hugging as ground strike aircraft do,or protected by terrain as in kashmir mountain area where s-400 would be less effective but not over the plains of punjab-sindh.) of all pakistani forward airbases from 150-200 kms within indian territory.It can shut down Erieye AWACS support and refuellers from 200-300 km within indian territory.Even if S-400 doesnt shoot down a single fighter itself,if it just takes out the AWACS PAF will be fighting blind,while IAF would have AWACS support.Jf-17s would have no chance against MKIs without AWACS support.Forget rafales with meteors.
Now among the solutions proposed -
1.Drone swarm being proposed here is really mostly attractive in paper.Cheap drones have bad range and cant penetrate hundreds of kilometres of indian territory without being shot down.Spyders and akash would easily shoot these down,but mostly AAA guns will be the most cost effective.Simple ZSU-23 and L-70 bofors can deal with these,and even HMGs might stand a chnace.
What you need are essentially large numbers of loitering munition drones like the israeli HAROP which have been successful in syria.But these are not 'cheap'.India bought 8 harops for 100 million so price is 10-12 million(add inflation to 2009 numbers) each which is 1/3rd the price of a brand new Jf-17 fighter for a one time use throwaway weapon which can still be shot down by AAA.But yes if bought in hundreds such systems can successfully penetrate a SAM defense.I dont know if pakistan has access to such technology from china,because the israeli one isn't available.
The recent deal of 48 UCAV from china is a good move.These drones however are not suicide drones but small Low RCS launch platforms with a couple of missiles.They lack firepower but would complicate matters for IAF and give PAF modest penetration capability.Main thing is only 48 are being bought while the Indian deal for s-400 comes with 6000 missiles .Even leaving out s-400 escort SAMs , if just 2 of the 5 s-400 systems being bought are forward deployed against pakistan in indian punjab and gujarat,you have 2400 s-400 missiles facing pakistan.(3 more protecting delhi core area,mumbai core area and passageway to south india and other on chinese front).Saturation is near impossible against such numbers.
2.Another solution being talked about was ababeel 'MIRV' missile which was the most unrealistic.First of all this is not a MIRV missile at all,there exists in the world no MIRV SRBM/IRBM technology(unless pakistani technology has surpassed superpowers).Neither USA,Russia or China has been able to deploy such tech.MIRVs are employed on huge complex ICBMs and are used to evade BMDefences and to attack soft targets like cities.They are certainly not used against a mobile SAM system like S-400.No independent source has acknowledged ababeel as a true MIRV missile.
3.Babur cruise missile .For me this is actually a workable solution.As far as i know Pakistan currently deploys 23rd and 26 missile group each with around 200 babur missiles.(96 on TELs and 96 reloads).Thats a very good number of around 400 baburs for use.A portion of these can be used for local saturation attacks.Limitations of this tactic would be - India deploys similar numbers of brahmos and babur is the only real capability pak have to strike targets inside India as PAF can no longer do that over indian airspace.Use up too many baburs on s-400s and will be left unable to answer brahmos and SCALP storm shadow LACM.2nd limitation is since babur is subsonic missile its vulnerable to SRSAMs like Spyder, Akash, Barak or even CIWS.But it has advantage of terrain hugging approach which means s-400 can only detect and attack it at modest range of 40 kilometres.
Thus solution is to increase pressure on s-400 increase babur numbers.Deploy more missile groups.
4.Simply either buy S-400 yourself.Or wait for 5th gen fighter with good ECM capability.Around 50 of such fighters will even things out a lot.
Pakistan has time.There will not be any large scale war between India and pakistan,now or possibly ever.Too much to lose for both sides and the world.What S-400 does is create complications for Pakistan's rhetoric on battlefield nukes as forward deployed s-400s can shoot down nasr's easily even from 150 kms within indian territory, being originally designed to shoot down pershing IRBMs and similar weapons over europe.So even though there would not be a real war,it strengthens india's boldness.
The main tactical problem it creates for pakistan is not of a full fledged war but rather it gives India an opening to do what it wasn't sure it could do with impunity until now.Carry our airstrikes on terror camps in case of another mumbai like attack.If S-400 is in position and rafales carry out the attack PAF will not be able to really stop such an hit and run attack.Rafales with Spectra and low RCS would evade sams relatively easily.S-400s would keep PAF response in check and AWACs away.Even with AWACS against meteor armed rafales it would be difficult.But without them it would be suicide.That is the main short term advantage once rafale and s-400 infrastructure is in place which would take another 3-4 years at least.
Paf would have to respond with 5th gen fighters or S-400 itself or concede this advantage.Thats my view of the situation.