Normally the tray goes down first, and then everything else on top of that. Would think it would be rather difficult to simply replace the tray unfortunately. If you can get the rest of the panels (if acrylic) out in one piece, you may be able to reinstall after replacing the tray. Best of luck!

Is it white acrylic base and lining? If so, the whole thing will need to come out because there is a small 10-20mm lip up behind the liner that will be fully siliconed in.

Yes, thought so. I don't think there's an easy way of removing the tray without taking the panels out, which would probably mean replacing them...

If it was from something falling on it and cracking it then it may be an insurance thing you can look into.

And with a bit of luck, no excess on bathroom bits ...

Complete new Showers including trays are pretty cheap these days. It may be tempting to just go out and get a whole new thing.

But most of the cheap ones mean built cheap, and you may end up having the same thing happen in a couple of years. It is my understanding that the showers with plastic trays (complete units) can be put in without building consent. This may be why they so popular.

I can't handle the plastic, not only can they crack, they scratch too, and after a few years can start looking dirty.

If I was redoing my shower today I would probably opt for a stainless steel type. They old fashioned, but they will last a lifetime. Otherwise even better, if your house is on a concrete slab, get it done professionally out of concrete & tile.

Is there an issue with tiling in a wooden framed house?

Don't want to depress you, but I had a similar experience as chimera. Floor replacement job plus wall re-lining with moisture proof plaster board. 

At least the leak into the ceiling in the room below stopped!

Our recent refurb included three bathrooms in a timber frame/brick veneer house. Two upstairs on timber floors required a waterproof membrane system, with the shower drain designed as the lowest point in a sill-less shower. The third bathroom, was on the ground floor concrete slab so the shower couldn't be built lower than the floor. It also required a waterproof membrane, but also had a floor drain in addition to the shower drain and the shower has a sill.

They're pretty strict now days on the design and certification.

I was in a similar situation last year, tried to get the tray only replaced but didn't have much luck finding the size and they were saying liner has to come off too and there is a risk of liner breaking etc and finding the exact size and type tray was also a challenge.  Ended up buying a Clearlite Sierra Shower, changed all the plumbing and waste had to be moved too as i got a slightly bigger shower. Also, GIB had to be replaced when liner was pulled, go with Aqualine GIB only.  One more thing, make sure the installer cleans the base before putting the tray and the area around the waste is packed properly using concrete not loose rocks etc. or gap 7.
Getting tray installation right is more important I think. 

Total cost ended up roughly $3000 I think. Only thing which is a bit of hassle is coordinating with different tradies, plumber,builder type of person to do the GIB etc and the shower installer then again plumber to put fittings back. Other option was bit expensive to contact someone who can do everything like some shower installers supply and install but maybe worth it as I found this process full of stress and time taking. Shower was this one http://www.trademe.co.nz/building-renovation/other/auction-1389871379.htm but you can get it for a better price. 

I've learnt it's all about getting the right installer but can be challenging as they want a plumber to do the tray.