Lot's of things involved here:
1. Baron's on destruction text: It goes first. The card flips.
2. Target and text entering play with "When this card enters play" text on it. I believe that goes first right? We keep the chain of events going until there is a break, then go to the next effect waiting to happen.
3. Does Sentinel Tactics have to be in play for it's trigger, that is already activated, to resolve?
The Case Evidence:
The new list of rules MigrantP put up has a ruling that cards that go under another card after their response to destruction text has activated, even though they lose that text upon going under another card, still process their effect.
The effect of Tactics, has already triggered and is "in qeue" does it still require the card text to be in play? Cards going under other cards don't, I don't see why cards leaving play wouldn't either.
This is different from cards who are dealing damage and leave play, since there is no longer anything there to deal damage, or an action that is mid-process getting interupted, like an environment effect that leaves play because of BeeBot. The effect has triggered, and is wiating to resolve.
I don't see how there could be a difference between a card losing its text from going under Savage Mana but still, but having the already triggered effect resolve, and this situation.
Because of that I would say the extra power would occur after the flip.
On a side note I think this makes sense with the Informant ruling that you can't stop her effect by destroying her as well, but that is a different case adn I don't want to open that can of worms, just point out that we know you can't stop it, and MigrantP's post seems to go along with it.