With the life estate you have three values that can be determined:
1. The value of the Life Estate
Actually exists as of the date of value
2. The value of the Remainder interest
Actually exists as of the date of value
3. The value of both of these held jointly, which is the Fee Simple interest.
Does not exist as of the date of value - Purely hypothetical
The fee simple interest does apply. The two can get together and sell the house in fee simple title if they both agree to sell their interest together.
This is what I like to refer to as "forcing the ideal."
For example, when many appraisers appraise properties with "problems," say systems in a home don't work or house is gutted, there seems to be a need to appraise the property to an ideal, such as determine the "subject to completion" value. The starting point for any appraisal is "as is," i.e., what actually exists. Some clients may have different requirements, but that is a client decision, not the appraiser's.
With regard to the issue under discussion, the fee simple does not apply, unless the client needs to know those particular hypothetical property rights appraised.
When doing an appraisal for such a sale, the fee simple interests are not hypothetical. The two can also come together and take out a mortgage jointly on the fee simple interest of the property. The fee simple interest, when they do come together, applies. In such a case, if the house is foreclosed on, both parties are responsible for the mortgage and both interests are foreclosed on with the lien holder taking fee simple title.
Theoretically, they could come together at a future date, but clearly and legally are separate as of the date of value.
This is not only true of this particular issue, but with any property owners. The owners of a leased fee and leasehold interest could come together and agree to combine their interests to create the fee simple interest. Two owners of abutting vacant land can come together and combine their rights to create one parcel. The scenarios are limitless.
In whatever scenario occurs, the appraiser must properly identify the rights being appraised, and if they don't exist as of the date of value, identify that the rights are hypothetical.