Well for starters you might not see as big a GOP win in the upcoming mid-term elections due to the sympathy vote. Don't know if Clinton's assassination would be enough to totally derail the Gingrich Congress, though that's certainly a possibility. At the very least the GOP's not going to win as many seats in the 1994 elections.
As for Al Gore running in 1996 and potentially 2000, I believe since he would serve 2 days over half of Clinton's term he would be prohibited from running in the 2000 election due to the 25th Amendment.
The real question is, assuming the GOP retakes the House and Senate in 1994 (albeit by a smaller margin due to the sympathy vote). Will Al Gore be in a position to win in 1996? Keep in mind that the man's not the most inspiring speaker (or at least wasn't back then, still isn't IMO). Furthermore the Federal Government Shutdown of 1995 was a close run thing for the GOP, had Gingrich not stuck his foot in his mouth popular opinion might not have turned against the GOP. There's also the question of who Gore picks as his VP, I'd imagine he'd probably go for a Northern Democrat, Paul Tsongas perhaps?
Come the elections of 1996 I'd say that it's a safe bet that Gore would be facing a far more serious primary challenge than Clinton did in 1996. Futhermore, without Gingritch shooting his mouth off in 95 the GOP candidate pool might be bigger as well. Weakened by an internal challenge and faced with a better GOP opponent than Dole (Cheney?) Gore's not a shoe in for victory in 1996...