I think a model like Bayern where there is high energy in the team, a well rehearsed system and very little star-like players who have complete freedom is achievable post Messi.
Every manager would kill for Messi AND a model like Bayern. Our team has no high energy, no system, no pace, no wingers. Any quality players that come here to play a free role would fail terribly. A team is supposed to be diverse and complimentary. Just like I wouldn't want 10 Gnabry in my team. A player however must contribute heavily in the role he plays, in this case Messi has always been very eager and capable of doing so.
And the notion of having Messi not drop deep is not feasible. He aint gonna wait in the box all day. The idea is have him anywhere in the pitch and not have him tracked by opposition team. Also, the teammates always have a choice to not pass to him all the time. If so, Setien didnt do a great job in regulating them through instructions. But you are too focused on him dropping deep and not seeing the bigger picture. A free role allows you to be everywhere on the pitch; Messi is everywhere on that right side of the pitch. He drops deep occasionally to just draw them out once in a while. It aint nothing. Otherwise he would be always in the most congested area doing nothing without the ball and they will know he's always present; it's extremely easy to mark. Heat map of his is fine.
And gosh, why would pressing or tactic be the first thing that comes to your mind. Get proper strikers and wingers first geez. Get younger players. You can't expect something to work out in a broken system. You cant press with our current team too. Messi is the last thing to change if you havent even tried the most fundamental things.