As Richard said, such fade-outs usually go over a repeated vamp. Rock bands tend to cycle that vamp as long as they think the audience can bear it, then the drummer plays a fill to cue the others into the final chord, which is then simply held for a couple of seconds (often with tremolo guitar flailing and more drum-roll filling), culminating in a fat unisono hit. Of course, most songs are arranged for playing live before being recorded, so it could be argued that the fadeout is more of an afterthought to get rid of such a live ending – which would be a bit ridiculous on a studio recording...
The Police are notorious for this: virtually all their studio recordings end with a fade out, whereas live it's mostly frantic jamming around until the end.
Thinking about it, the way many classical orchestral pieces end is actually pretty much the same...
This kind of ending can work with an acoustic group too, but it can also come over rather silly, if you haven't a big amplified sound for the final chords. It's usually better to not overdo it with the final culmination – better just start a ritardando at the last two chord changes, then emphasize the penultimate bar (e.g. stop the usual rhythm and just play crotchets, perhaps, if it's a dominant chord, split it up in two sus4 chords, two seventh chords, and then finally bring the tonic, rather more quietly.
What can also work very nicely, especially with acoustic instruments, is to stop playing chords at all in the final bars, and find some nice melodic hooks instead that lead to the final tonic.