I seem to recall from past interviews that Warnock has a bit of a chip on his shoulder about Liverpool selling him but I think his ire was directed more towards Benitez (and who can blame him) than Houllier.
If he has a chip about being sold, I would assume that's entirely aimed at Benitez, since Houllier just loaned him out to get experience....
I know Friedel had a good game against Everton but he's 40 next season and he will need replacing.
Why? Because he's 40? Get real. If he keeps making spectacular saves that keep us in games, then I'd keep him in the team. Being a Goalie isn't the same as being an outfield player, he needs to have good reflexes, and I've seen very little evidence that he hasn't got them still.
Also, he needs to be able to position himself and read the game ahead of him, neither of these will suffer from his age.
If he stays fit, and there's no indication he won't, then I'd keep hold of one of the most reliable, experienced goal keepers in the league.