Re: What if Kane didn't work out?
As far as writing Kane out of the storyline goes, I actually think it would have been pretty simple. It would've sucked and felt like an enormous letdown (since Kane's debut had about 6 months of build) but all it would have really taken to kill the angle would be for Undertaker to beat Kane's ass and send him back to hell where he came from.
Would there have been grander implications? It certainly was to the WWF's benefit that it worked out, both in that it drastically deepened Undertaker's character while also producing in Kane what was essentially an instant main eventer (until about the end of 1998 anyway, it was all downhill from there for him). Ultimately I guess Taker would've just moved on to something else while having his character seem like it had a major unresolved issue, and Kane would've been one of the biggest what-ifs in wrestling history.