Be hard to replace something that replaced the 1911! Big shoes to fill, however in my opinion it filled it for a few simple reasons that are well known.
1) NATO compliance ,everyone else in alliance was using 9mm.
(actually makes sense in regards to the alliance)
2) More Capacity and less weight/carry ammo ratio
(obvious)
3) Easier to Field Strip
(obvious again)
4) SA/DA (my opinion here is each his own - I love cocked and locked on 1911 - and do not mind either platform - Bit 1911 triggers are a dream)
Just to name a few. It is above all a proven platform, and has proven itself in the field for 20 years now. With that said I think any DA/SA contender would suffer the same criticisms that the M9 has.
Maybe a SA only 9mm on 1911 platform with 15 rd capacity could compete, but I doubt it. It would seem that the powers that be decided SA only is not the best choice.
So to the questions:
1) The M9 will remain the standard sidearm for at least another 6-8 years.
Affirmitive.....probably a lot longer!
2) Its replacement will be a US-manufactured gun.
Oh politics!.....don't bet on it!
3) Its replacement will still be chambered in 9mm.
It will either be 9mm or most likely a Photon Plasma Generator!
4) Its replacement will still be a metal-framed DA/SA design with a manual safety. Most likely with exception of Photon Plasma Generator..it could probably be polymer.....