1) This wasn't an "impromptu visit". The visit was already discussed. The timing was impromptu as Modi wanted to put a personal "touch" to this. Which actually makes a lot of sense if he wants to leave a legacy of peace starting directly with his name and from this trip.
2) Thank you Uncle Sam (about 60% of the effort), and the rest goes to the Russians, the Chinese, the Saudi
s and the Britts. Modi was under pressure from ALL sides to make peace with Pakistan. A thank you goes out to NS's awesome diplomacy also that resulted in this.
3) No one knows the future as there may be events that further the peace process rapidly (I'd hope), and there may be some unknown tragic events that might derail it (sadly, things have happened on each side before). But as a Premier of the second largest country (population wise and one of the top 5 economies), its reasonable to expect that the personal touch shows sincerity. You won't go see someone's family if you hate them.
4) I think the peace may be coming to this region (slowly of-course). I think an EU type of a solution will be put in place. India, outside of the external pressure has smart businessmen pressuring the government to create peace also, as they see tremendous opportunity in Afghanistan, Iran and other places through CPEC. So they don't want to remain behind. The Chahbar port is worthless when compared to the size of the market you get through the CPEC.
So all in all, a good progress for both India and Pakistan and for both the premiers to start this process with utter sincerity and connecting with each other through families. Hopefully, this would build long term relationships even in the future. Its much easier to call each other during issues comfortably and discuss at the highest level, than dragging feet through the media, the foreign ministers and like 200 aides. Good progress