I can't see Sony letting them kill him off that soon, they're going to want to keep him around for at least a few more movies.
I don't think Sony has any real creative input into what Marvel does with the character in their own movies. If his final appearance in say in an Avengers movie, theoretically they can kill him off (again!

) and have him "gone"from the MCU. Now Sony may be free to go right on making Spider-man movies on their own, but if Holland chooses that time to bow out too, then they're most likely back to rebooting it again.
More likely to be that they're proceeding on a 'One for us, one for you' basis and will renegotiate as they go.
Maybe, but I'm taking the optimistic look (dangerous, I know) of perhaps they wanted to settle the deal for the third film right away (so not to delay production) and while keeping their options open for the future with another negotiation later on down the road.
Yeah, I don't think Disney would be that stupid, since that just puts Sony in a position to play silly buggers again in a few years. It'd be a long term deal, set in stone to make sure this wont' have to be renegotiated all over again in 2 or 3 years. That i's basically just two movies says to me Marvel either wants to round the character out and move on, or they know Sony won't be relevant in 2-3 years.
If the Star Wars announcement happened more than just two days ago, then perhaps so. As is, that would have been a pretty fast turnaround (especially considering the deal was inked last night) so I doubt it.
So far as I understand, the deal Sony went for was Disney's original offer from a while back. Which means Sony were holding out for better terms. That they chose to accept it *now* just days after the SW announcement to me smacks of capitulation. I mean they couldn't even budge Disney down a single percent OR get any of the merch profits as I suggested back in August might be on the table.
Make no mistake, The Mouse was in the position of strength here, not Sony. I mean Disney can loose Spider-Man and just eat the loss of profit and investment and not even break stride, while for Sony going it alone is 1) more expensive since they don't have a co-financier 2) more risky due to their previous failed attempts at keeping this IP going and the absence of a larger mega-franchise like the MCU to buoy up the audience numbers.