when both the purchaser and vendor cannot agree on the terms of the SPA, the only solution would be to
cancel the whole deal..it has happened to me before..

6 months to remove a caveat?? usually it does not take so long if its a straight forward case so I believe the
vendor must be having an ongoing case with an ex purchaser so would you want to take the risk by going ahead with it? you may end up with nothing..

I mean by giving the vendor a free hand to cancel the SPA without compensation , its really a bit one sided.

why are you not seeking advice from your SPA lawyer??