The value of the investments in your ISA is added to your estate and may be liable to Inheritance Tax. Whether the fund is sold or the account holder's name changed is usually confirmed after probate is complete.
If the fund is held outside an ISA, the funds can either be sold or reregistered in another name (according to the probate details). The new applicant(s) will need to complete a new application form.
Target Funds are actively managed to lock in gains made in the early years. They use the portfolio manager's skills to select the right funds at the right time so that the asset split evolves towards the target date.