What happens if a key supplier contract turns out to be unassignable?

It depends on the deal structure. In a share sale, this generally isn't an issue, because the corporation that holds the contract doesn't change — you're buying the shares of the same legal entity the supplier already contracts with, so no assignment happens at all. In an asset sale, though, the buyer is a different legal entity, and most commercial contracts either require the supplier's consent to assign or restrict assignment outright, so a key contract can genuinely fail to transfer if the supplier says no or the contract's wording doesn't allow it.

Losing a business-critical supplier relationship partway through closing an asset deal is a serious problem, which is why reviewing material contracts for assignment restrictions is a standard due-diligence step, and why getting supplier consent lined up (or at least confirming it's realistically obtainable) before you're contractually committed matters far more than doing it as an afterthought.

If a key contract is unassignable and the supplier won't cooperate, your options are typically renegotiating a new contract directly with the supplier, structuring the deal as a share sale instead, or adjusting price to reflect the lost relationship. A Treadstone business lawyer can review assignment clauses before you commit.