Dying Hoya plant please help!

[icie]

I got this hoya plant from a plant convention a while ago (don't know the exact name since it wasn't labelled and the seller didn't know) and for the most of the year it was doing great. However for the past few weeks its been a slow descent to death and I don't know why. I think i may have over watered it once? (I generally just gave it a soak after it had completely dried up, but between me and my mom it might have overlapped once) But basically each branch is slowly drying up from the tip, with the leaves turning yellow and wilting. I've just been cutting them off as it happens, but I think the roots were permanently damaged or something.

I tried repotting the soil (using cactus mix and lots of perlite) and watering it a little more but it made not difference. I kept it in a kind of semi-lit area and I live in Southern California so it's a kind of dry, but it had been completely fine up until a few weeks ago.

Is there anything I can do to save it at this point or is it just doomed (I was thinking of maybe just cutting it to try and propagate at this point)

(I moved it to our backyard for these photos-maybe I should leave it there? It would get more light but also risk more heat since its warming up.)

 

[NigelJ]

Hoyas are tropical plants typically climbers in moist jungles/forest often epiphytic. So you need to give it similar conditions. High humidity and a well drained compost with plenty of organic matter, that allows some air into the roots. So perhaps a mix of perlite and leaf mould rather than cactus mix. Your leaves look to be short of water middle picture with wrinkles. This could be lack of water or too much water causing root rot. When you repot have a good look at the roots and see if there is healthy growth.
I would try and propagate cuttings and air layering.
I have a Hoya carnosa which is probably the toughest one. supposed to grow 16 - 29°C, mine has been down to 5°C lives outside in the summer in a shady spot, in winter it doesn't get water until the leaves begin to feel thin and papery. I have propagated this from cuttings several times and it probably needs repotting.
other Hoya species are far less forgiving and require close attention to their requirements for hunidity, light and temperature. Although most seem easy to propagate.