First of all a diesel sub can't sail that range without coming to the surface to recharge,which in wartime is when they are detected and its usually suicide.AIP increases the time it can stay submerged a bit more but nowhere near nuke sub levels.Here you see it made port calls.
Thats why for long range ops diesel subs are of very limited value as in wartime satellites ,listening posts,maritime air recon will easily pick it up moment it surfaces and after that its finished.Diesel subs can't outrun ASW surface ships either because they lack the speed of nuke subs and if they try to go fast their batteries produce too much sound.Thats why diesel subs never serve as carrier group escort.
Diesel subs are good at one thing and they are very good at it.Short range ops near ur territorial waters,lying in ambush for enemy ships in shallow waters..in this role they are nearly undetectable(more stealthy than nuke sub) and deadly.Its their niche.
So indian navy doesn't need to bother about chinese diesel subs at all as in a real war a chinese diesel sub sailing from china into indian territorial waters=suicide.For ops in the IOR ,only PLAN nuke subs are of any value.And most of those are obsolete or noisy.Plus with data sharing with USN we pick them up much before they enter area of interest.