It's not the end of the world
Obviously the view is not pretty but luckily Sabean has a number of players on the bench who have been and could be starters on at least a limited basis. As maligned as Tucker is (it's not his fault the Giants chose to give up a draft pick for him), he is a pretty good hitter vs. RHP, .264/.347/.437/.784 with 100 HR in 3106 AB, or 1 HR every 31 AB, or about 20 HR playing 162 or so games. When Carlos Beltran was out early one season, Tucker hit so well that Kansas City was contending even though Beltran was out. He would be good in a platoon with a strong platoon RHH like Grissom. Unfortunately, with 1 maybe 2 outfielders out, there's no one to platoon with him. However, he tends to hit better early in the season then peters out, so hopefully he can heat up now when we need him, then rest up when Alou and Bonds come back, and be ready to heat up during the playoffs.
So, if Moises go down, I guess that means that Niekro will probably come up and platoon with Snow while Feliz is busy in LF, unless the Giants think that Linden is ready to get some ABs (doubtful). Assuming it is Niekro coming up, that means Feliz in LF, Grissom in CF, and Tucker in RF with Ellison and Torcato backing up. I can see Ellison getting some ABs vs. LHP in RF (or CF with Grissom shifting over to RF) but Torcato probably won't get the call to play LF much vs. RHP as long as Feliz continues to hit them RHP like last season: .269/.301/.483/.784 with 15 HR in 331 AB, a 30 HR pace whereas before he was stymied by RHP and was strictly a platoon player, killing LHP.
The lineup would be Durham, Vizquel, Snow, Feliz, Alfonzo, Grissom, Tucker, Matheny. Not great but if Durham, Vizquel and Snow can get on base a lot like they normally can, Feliz and Alfonzo will be coming up with runners on base often and get a chance to drive in a lot of runs. If they can hit like they've hit in the past, the offense should be decent enough to keep the team in games. Unfortunately, the Giants as a team has not been driving in runs during the regular season play, they have been leaving a lot of runners on base.
The starting pitching has been OK thus far so the main thing that will determine how well the Giants do while their sluggers are ailing is their bullpen. The bullpen need to steady themselves and stop giving up so many runs. If they can be as good as they should be, the other teams will not be scoring that many runs, giving the Giants offense a good chance to win without scoring a lot of runs, kind of like how the Dodgers won in the 60's with their great starting pitchers, Koufax and Drysdale.
And the defense has been sparkling the first three games. The pitching should be feeling good about allowing batters to hit the ball to one of their fielders, knowing that they will get to the ball and make the play. That type of confidence takes time but the display of Vizquel's artistry has been an attention getting already so it's only a matter of time.
Lastly, the Giants play Colorado 6 of the next 8 games, plus the Brewers in 9 of 15 games. Plus the Dodgers again, Padres and the D-backs, 2 games each. None of these clubs look to be juggernauts during the early season plus we also get 3 games with the Pirates at the end of the month. That's not a really scary schedule for now, so the Giants should not be pushed down to the ground like they were at the start of last season. Plus Alou will hopefully be back in less than two weeks, assuming they retroactively DL him so he misses only 13 games. Their offense is adequate enough, I think, to support our starting rotation, we only need the bullpen to start pulling their weight.