B744 (and the classic too!) can dump gas. If it's a max weight departure (397 ton) and you need to come back then, depending on your max landing weight (they vary 285 - 295 ton), you will need to lose about 100,000 kilos of kero. Time taken to dump would be about 55 minutes. If you didn't have the dump facility it would take many hours to burn the gas off!
If you don't have time to dump (e.g. you are on fire) then obviously you are going to have to land over the max landing weight, after which maintenance have to do a heavy landing check. As you can imagine at these weights you would chew a bit of runway and to make the problem worse the ref speeds at that weight are above 180 knots (max KIAS for flap 30) so you have to use flap 25. You can't do an autoland either.
