I think 25s seems like a reasonable gap, joking aside. As well as to what could be realistic for him to gain after his attack, as to what could be enough for him to hold. I think in order to catch him on the Mur with a 25s lead, they would need to start early. So who's going to start early with Alaphilippe in his wheel? I think Evenepoel is better than most (if not all) to sustain the effort on the Mur after having gone on the attack on the flat. It wouldn't even be unthinkable that some of the chasers might die on the climb sooner than Evenepoel if they chased hard on the flat. Anyway, i think Alaphilippe's presence might be enough of a deterrent that a 25s gap could be enough.But are you really expecting Remco to be so weak that he only has 25s?
I actually think he can win solo, but not by only having 25 seconds at the base.