Let the dice fall where they may:
I don't know. It depends on the game and current story arc. I feel that D&D is meant for a heroic game, and that would make me fudge some rolls in such a scene (I won't betray players for trying something cool).
The same goes for Adventure!, a pulp action game.
On the other hand, in Vamire, or (to a lesser extent) Trinity, I play a fairly realistic game (you could say gritty). Then, I would let the dice fall. Most of the times. (see below)
The problem is when you fudge, where you fudge. When you fudge once, it's tough to explain why you didn't fudge in a different scenario, when the plot broke down, or a PC died.
Recurring Villain:
I feel that a strong villain is a plus in a good campaign. Sometimes they have to come back. I agree that players start to hate the villain, and sooner or later he'll have to die. But the players invest far more in his death than in some nameless slub.
When the RV gets away, that doesn't mean the players lost. Imagine Blofelld from the Bond movies - he was thwarted everytime. Still, when you saw the chair, the hand and the white cat, it added excitement to the film
When I see the possibility for a recurring villain, I
might fudge the dice for him to get away and see the players' reaction. That's where I'd fudge in a realistic game (and when I really enjoyed or admired a player's game).
So, I'm a fudger, and a recurrer. I'm a bad DM, it seems...
B
P.S.: Note that the WW games I mentioned are far less roll-heavy than D&D (imo).