Allegri hasn't been out for three years, it's been season and a half since he parted ways with Juventus. Two years sabbatical it will be this summer, but not too big of a deal. However, I definitely wouldn't want him to take over. He's absolutely not the kind of guy to play the football we want.
As for Ancelotti, that's absolutely the same as hiring van Gaal and Mourinho. Manchester United must go for young progressive manager like Nagelsmann. I'm really not sure there are many like him. Guardiola, Klopp, Tuchel, Pochettino, Nagelsmann and maybe Rose will be cream of the crop for years to come. Constantly missing out on each of them is crazy.
And if club hierarchy thinks, as some here do, that Ancelotti is better option because he has more trophies than Nagelsmann, well then there is something fundamentally flawed with this club.