One of the least popular deaths in the Highlander TV series was that of Richie Ryan; there are still people writing "Richie Survived" fanfic, and trying to find ways for him to escape his fate. I've got one for them...
In Ian M. Banks' Culture novels the Culture discovered Earth in the 1970s (The State of the Art), took a look, and decided to leave us to get more civilised. But we know that their Special Circumstances agency recruits agents on primitive worlds, often ones that have had no overt contact with The Culture (Use of Weapons). Worlds like Earth, for example. So let's say that Special Circumstances hears about Earth and comes headhunting (in the employment sense) in the nineties, and discovers the existence of immortals. Someone who can survive being shot etc. would make a wonderful agent; there are a few problems, of course, such as not being able to make use of any of the Culture's advanced implants (I'm guessing that a regenerating immortal would reject them) or plastic surgery, but on the whole it would be a definite plus.
Now The Culture doesn't want to take anyone off Earth who is likely to be missed, but they have good cloning technology. As in being able to regrow someone's body from their head after they have been decapitated (again in Use of Weapons). Given the number of Immortals decapitated every year, it shouldn't take too long for them to be able to get hold of a head or two.
So let's assume that a few seconds after Richie was decapitated his head rolls out of view, and is promptly displaced (transported) up to a Special Circumstances ship, placed in stasis, then connected to life support. Months pass as the body is regrown, and eventually a new Richie Ryan is born. Problem solved, and we can have a Richie Ryan: Culture Agent spinoff series.
The snag, I suspect, is that he's no longer an Immortal - his killer got his Quickening, and I can't see any obvious way to get it back, unless there's some sort of residue left in the head, and if that was the case the heads of all of the decapitated Immortals would presumably be growing new bodies, which is something we don't see on the show. But this snag apart it's one way to get Richie back into play. Or any other character from Highlander who is decapitated, of course. And whoever it is will still be a highly trained swordsman and warrior, in all probability, so very useful to Special Circumstances.