There is no "rule" pertaining to making or accepting an offer of purchase. The developer is not interested in what your business is worth and will probably offer nothing for it -- he will offer only the "fair market value" of the property (or less if he can get by with it). The Fair Market Value is the value established by the market place: what a willing buyer will pay and what a willing seller will accept. A qualified appraiser can estimate the Fair Market Value by analyzing the sales of similar properties in the general area. His work will not include any valuation for your business. The idea is that your business can move down the street to another location and continue on.

If your business is somehow unique and cannot be moved to another location, or if the cost of doing so will be prohibitive, then you just don't sell. It may be that if the developer needs your property badly enough, he will offer more than the property is otherwise worth simply because of the need. If he does so, it won't be a purchase of the business or a payment to reimburse you for damaging/destroying your business -- it will be an adjusted purchase price simply because that's the only way he could get the property.

If you want to seriously consider the developer's offer, you should confer with a good real estate lawyer in your area for assistance in negotiating the price and making the transfer. It is risky to enter into such transactions without a lawyer unless you are experienced enough to undertake the effort alone.