The appraiser is not being asked to appraise the transaction, he is being asked to appraiser a property right. When banks lend on life estates, they typically have both the life tenant and the remianderman sign the mortgage, meaning that the mortgage is being secured by the full fee simple property. Thus, the lender is likely requeting and needs an appraisal of the fee simple property interest of the subject property. This can be done with no problem as long as the appraiser provides the proper disclosures and no life estate comps will be needed. I need more details, but in this case it appears that such an appraisal could be done "as is" without needing to use a hypothtetical condition, since as of the effective date of the appraisal, the property appears to be a fee simple property (based on the limited information provided by the OP) and the life estate will not be created until after closing and after the appraisal effective date although the appraiser must be sure to disclose the results of his analysis of the sale contrract, which would indicate that the purchase contract is creating and transferring a life estate.