You are of course again assuming that you would have that much time to play with, and that all the Wizard's spells are breaking off your cleric like water on rock. With touch attack spells that can be delivered at a distance and do > 250 points of damage or so, no saving throw or SR, its a matter of you (or anyone else who ****es a wizard off) making one minor error. A level 20 cleric will likely have ~200 hp at most, unless you are twinked out the wazoo. That is even a high estimation. I dont roll PnP twink style DnD. You either have a few really good items, or alot of magical trinkets.
The old "jab until you wear the opponent down" strategy works well until you encounter an opponent that can slay you in one shot. Then its like Mike Tyson fighting a bum in the 80s. A pile of ashes doesnt heal itself lol.
I am not arrogant enough to claim a 100% victory chance, which is statistically impossible given the nature of DnD to begin with.
My original point - A wizard can still slay ARMIES of melee at higher levels. There is no balance of power in DnD, and thats why I like it. People complaining about one spell having too much power should roll up a caster and see what happens when they get too comfortable with the "firewall everything" strategy. Complacency kills more wizards than any prestige cleric build. Not being prepared = dead.