First is to fix the UFO up enough to have it slowly fly off -- feasible for multi-engine ships
Second is to cut apart the UFO into pieces if it's too badly damaged (all power sources blowed up); like with smaller ships -- basically junkyard stripping it and crushing it into a cube.
Third is to obliterate the entire crash site with a UFO laser -- I'd imagine unfeasible for any of the larger ships; plus the huge flash of light and explosion would attract attention from human authorities.
Fourth is to pick up the damaged unflyable ship with a bigger UFO
From my point of view, first of all, it's important to remain consistent with the game's design, any UFO targeting a crashed spacecraft like that should appear in the Geoscape and behave like any other UFO: following a mission (i.e. Alien Recovery). I see three viable options, chosen at random when the mission is generated, which require different types of UFOs:
1) Repairing the crashed craft would require a special Recovery UFO (I'd make it Medium size, since those are rather uncommon), which would swoop in from space, land on the same spot as the crash site and 'erase' it and take off after a few hours.
2) Salvaging the crashed UFO could require a Supply Ship (or something else, since those are prized targets to catch landed, and the mission could be exploited). If it were a Recovery UFO, this case would be no different than the previous one. This variant would take approximately the same time as 1), perhaps a bit more.
3) Obliterating the crash site would likely require something like a Terror Ship for medium-sized and smaller wrecks, and a Battleship for larger ones. The mission craft wouldn't land at all, and instead hover over the site for probably less than an hour, 'erase' it and fly out.
The fourth suggested case seems pointless to me, since a damaged, air-unworthy UFO would either be repaired or salvaged. Not to mention the fact I doubt the aliens would go through the trouble of dispatching a large UFO to haul away the average small/medium (the only kind I see being hauled) spacecraft. And at any rate it'd work like the third case, since the transporting craft probably wouldn't land to grab ahold of the target via tractor beam or whatever.
Finally, of course, the aliens would gain points whenever they successfully complete any form of this Alien Recovery mission.