Fallout: New Vegas
Likely to be dethroned? If Fallout 4 is any indication, no, not a big chance. That would require them to improve their writing, their world building, their quest design, and that they don't jump on the Games as a Service train anymore then they already have done.
It could possibly be dethroned by Cyperpunk 2077, depending on the direction CD Projekt takes with it.
Sid Meier's Pirates
Don't think it will be, even if devs try. Don't think they understand what made it so good. The useage of the map, different time periods, the silver train, the treasure fleet, the career building, the highscore list, etc. Maybe Mount&Blade 2 could have some of those influences, but it's probably to multiplayer oriented for that.
Jagged Alliance 2
If Firaxis continues with XCOM games, then perhaps. XCOM2 had many similarities with it
Monkey Island 2
Not really. Don't think there's an audience large enough, with the patience required for these games, for it to be realistic to hopefull. It would require a Witcher III class game to enter that genre, without anyone expecting it.
Portal 1
Could happen, definitely think that. There's a market for that kind of game, and there's plenty of devs with resources enough for it.