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no (not anymore, that would have worked up until M10)

here is a detailed breakdown:

when blockers are declared and there are multiple blockers blocking a single creature (such as in this case) the attacker declares the order in which those creature will block (in this case Archdruid, then Sentinel)

after that Turn Based Action the Active Player (the one whose turn it is) gets priority
after he passes that priority the Non-Active Player gets priority and casts Bandage
both player get priority and pass, Bandage resolves, setting up the prevention shield
after that both players pass again, and the game moves on to the combat damage step

here no both players declare how their creatures deal damage
the attacker has to deal at least lethal damage to the Archdruid (2) and can then deal the rest to the Sentinel. since he knows about the Bandage he will most likely assign 3 damage to the Archdruid to kill it, and 1 damage to the Sentinel
the defender has no choise but to assign 2+3 damage to the attacker

once that is decided combat damage is dealt, SBA move the attacker and the Archdruid to the graveyard and leave the Sentinel surviving as a 2/2 with 1 damage marked on it

then the active player gets priority, etc.

he has to play that in the "declare blocker" step as well
noone can respond to assigning or dealing damage

he'd have to play 2 Bandage to save his 4/4 attacker (or some other way to prevent 2 damage)

because all damage is dealt at the same time
at the time it deals damage the Archdruid is still alive and well