If there is a conditional contract, will the buyer want a contractual right to withdraw from the purchase is a major problem occurs prior to completion?
Why might the seller be unwilling to agree to this?
Yes.
The amount of protection given to the buyer depends on the original reason for imposing the condition. If the condition is a requirement of the buyer, e.g. buyer's shareholder approval, then the seller may argue that the buyer should assume the risk of any delay