There is none that makes sense really. I mean if they had done it some other way it would have ended up stretching the boundaries of what is credible. So in retrospect killing off Bobby like they did was a mistake.
I haven't read the other suggestions in this thread, but I can stop right here. Basically, this.
In past discussions, "solutions" usually involve some scenario where Bobby didn't really die or was resuscitated, before being hidden away to recuperate. It doesn't work. Hidden away for what purpose? Katherine was dead; there was no more threat to Bobby's life to warrant hiding him. Who hid him away, one of the Ewings? Then why did we see every one of them
privately grieving for him? Bobby himself made plans in the event something happened to him? If he was aware his life was in danger, why was he dumb enough to stand, exposed, in a driveway in the first place?
DALLAS had done the "back from the dead" story successfully twice, with Dusty and Mark. In both cases, though, we didn't see them die; we were only told they did. We watched Bobby die. We watched the Ewings grieve and deal with Bobby's death. Any scenario where he returned would have been the hoariest kind of writing, even for a soap in the mid-80s.
After definitely killing him, if they wanted him back they either needed a wizard or to pretend it never happened.
In retrospect, I think they should have just left him dead. Yeah, DALLAS wasn't the same without him but DALLAS was barely DALLAS even with his return. The damage done to the show's credibility with any return scenario wasn't worth the payoff.