The discussion was over IF Milner leaves, so in that sense Milner is already gone for the purposes of the discussion. Sidwell has been deciding between Fulham and West Ham. If Fulham don't want him then I'd say West Ham will get him. Either way, even if Sidwell is here next season, MON has consistently shown that he doesn't trust him in the side, with how sparingly he has used him (and any sub).
If we end up with £25m for Milner then you can't tell me we won't use some of that to bring in a Milner replacement. If you do think we won't replace him and will instead use a player from the playing squad that hardly played last season then you must have zero faith in O'Neill to the point where you will offer preposterous scenarios in your quest to put him down.
You can't hypothesise a situation where Milner has left the club then conveniently use 'currently' to pick his replacement. If he leaves then the situation changes. After all, "currently" he is a Villa player.