Just FYI - you are mixing up the terminology - a trust has a successor trustee. An executor is the term for the person who administers an estate based upon a will. The beneficiaries of a trust or the heirs of the estate can decline to accept the timeshare ownership. The steps required to legally transfer the ownership to someone else (via a sale or gift or deed back) will differ if it is a trust or a probate. With a trust, the successor trustee can sell or gift the ownership to anyone. Not sure why you believe that MVC would not accept a deed back. It is my understanding that the only requirement for the MVW deed back is that the MFs are paid current, which would be paid by the trust assets. If it is a probate, the executor needs to seek court approval to do any legal transfer of ownership of real property. That would include a gift transfer to anyone. The estate pays the current MFs prior to transfer of ownership to whomever is accepting it.
If you are asking what happens if the process of sale or gift takes more time then what happens regarding the MFs, yes, they need to be paid by trust assets until the ownership is transferred. If the successor trustee never transfers ownership to anyone, and the trust assets are dissipated, then it is no different than when a person defaults on paying their MFs. The unpaid MFs are considered bad debt of the HOA and allocated to the remaining owners to cover until the property is foreclosed.