Firstly, as you say the wall is not covered under YOUR insurance policy. Damage to boundary walls is excluded in all house policies, unless there is damage to the main house from the same cause at the same time etc etc - read the policy and exclusions.
I'd be more inclined to consult a solicitor. Your posting is not too clear (at least to me) of the wall (your wall) was built on your property by you or a previous owner. It is not clear if ths is a free standing wall, or a party/party wall of the warehouse. The warehouse was surrounded by a fence and trees. Who owned the fence/trees? Who owns the land that the stumps are now on? If warehouse owner owns the land and the trees, then he probably did not need to consult you before cutting them. Mind you, he should have obtained a tree felling licence if they were big trees and not an immediate danger to health and safety.
The owner of the trees may have a legal liability for damage caused by the roots. This is a legal question though, with the final decision being that of a judge. The only thing is, law is expensive, even very expensive and even prohibitively expensive if you lose the case.
If owner is offering to buy blocks and ye get ye're own labourers to rebuild - what's the problem? Can you not simply agree with him that you will knock yours and have it rebuilt? It will cost you something, but you will have a new wall and cheaper than a court case!