Mission 141: Kill Sal Marcano
Things to do before facing Sal -
Finish any of the optional missions you wanted to do. Technically you can run these afterwards as well, but they get even buggier.
Go shopping. There's nothing else to save your cash for, so stock up on explosives, guns, ammo, armor, and perks. The fight inside isn't that grueling- way quicker than the steamboat or the boxing gym, but there's no reason not to go all-out.
Once you're checked and prepped, go see Donovan, then drive out to the casino.
There's some scaffolding to the right of the main entrance- use it to gain access to the second level.
From here you can easily take out the guys on the upper floor, and have a vantage over the guys on the lower. Clear the room, then take out the minor wave that enters when you trip the check point.
From there, follow the objective marker, picking up a medkit if if need one.
Collectible Alert: There's a Vargas on the couch here. Just chilling.
The car here is begging to be driven up the jump ahead, but if you still have some tacvest intact, skip it.
Instead take the stealthy approach- there's a lot of guys up ahead, and anything you can do to whittle them down helps.
Pick off the wandering goons at floor level, but when thing get hot find some stairs. This will enable you to pick off the machine-gunners protected by the central corral.
Just be careful when you break cover- there's lots of guys with powerful guns here. Also be careful of Giorgi in his skybox. He's the single most dangerous element here, but he can't cover the whole floor- so either stay in his blindspots, or make him a priority. Once you've cleared enough guys, a smaller second wave will emerge from the stage door. Execute them, then either storm the office (now filled with a sniper team), or pick off the snipers from the balconys, and storm the office after.
Either way, it's time for a chat with your old pal.
Collectible Alert: Vargas in Giorgi's office.
Cutscene ol' Giorgi to death, then ascend for a long chat with Sal. When the cutscene ends, if you want to kill him yourself, shoot quickly, otherwise he takes matters into his own hands. Either way, go back down the elevator, and be met for a chat with a distinguished elder gentlemen. The two of you come to terms, and now it's time for one last drive out to chat with the Padre.
Also, if you have the radio on, you can catch The Voice's last broadcast.