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Just a little note. I found debug symbols for Unity3D and therefore was able to find out that it crashes in  crnd::crn_unpacker::unpack_dxt5

Fortunately, this code seems to be available on the net:
https://github.com/toji/webgl-texture-utils/blob/master/crunch/crn_decomp.h

bool unpack_dxt5(uint8** pDst, uint32 dst_size_in_bytes, uint32 row_pitch_in_bytes, uint32 blocks_x, uint32 blocks_y, uint32 chunks_x, uint32 chunks_y);

So pDst is an array of pointers that gets filled by the unpacker, some of them being possibly NULL because allocation failed, as you suspected. 
In line 

uint8* CRND_RESTRICT pRow = pDst[f];

there needs to be a check:
if (!pRow) return false;
to fix the crash. I can add it in assembly code, maybe the game then will at least shut down properly.

I will try the method to expand memory in the evening, nevertheless the memory management of the application should be able to trim the cache automatically in order to not hit the 2GB barrier imho. So I'm looking forward to the new version which supports reduced cache size.