Oh no, what a shame re: the saki monkey.
Paix ..... yes, the geladas are just behind the meerkat enclosure, and also behind the birds of prey display area.
I'd hate the geladas to go (so would my daughter as she's adopted Junior) - think they're a great exhibit and a lovely family group, though I agree with Pertinax that their enclosure isn't particularly good. It's been said before - quite probably by Pertinax - that ironically (given their natural habitat) the gelada enclosure is one of the few areas in Colchester that has no fake rock, even though it'd be quite appropriate for them !
Agree the patas monkeys are a sad display, though I find them fascinating and very striking all the same. That end particular corner of the zoo does seem to be neglected, almost an afterthought, in terms of its displays ..... the monkeys seem somewhat out on a limb where they are. The pygmy hippo area is also horrid and far too small in my opinion. I'd personally get rid of that playground near the mandrills and use the space for a new exhibit, e.g. the patas monkeys.