Sorry, I just can't justify the destruction endings to myself. Unless the DLC ending changes the outcome, I'm taking it at face value, and the destruction endings would kill EDI and the geth in addition to the reapers. Considering that Shepard helped both EDI and the geth become fully sentient beings, I consider that to be unacceptable losses.
And I just rewatched the synthesis ending. Normandy's engines don't get ripped off in that one, whereas they do in the control and destruction endings. I don't know why that is, but there you go. I went with synthesis, therefore my Shep's Normandy could survive. Besides, Normandy has a Scottish engineer, and if Scotty has taught us anything, it's that a Scottish engineer is the best asset to have on any space-faring vessel.
Basically, without the reapers to help rebuild the relays(since I'm sure I remember that they had a hand in the creation of them in the first place), the galaxy is screwed. To put it in Star Trek terms, they went from having a transwarp network to everywhere in the galaxy to being stuck with ships with standard warp drives. Humanity would be fine, they're within striking distance of home, as are the krogan. The rest of the fleet though, they're like poor Voyager, stranded very far from home. Frankly, if I were in the shoes of the quarians and asari, I'd be mighty pissed at humanity for stranding them so far from home.