If there is no deal. A UK CAA issued licence will be pointless. Until such time that an agreement between the UK CAA and other NAAs is signed.
Before EASA a CAA Section L licence was considered to be of a very high standard and getting other NAAs to accept it was reasonably straightforward. In theory we should be able to revert to that position but the machinations of politics are always difficult to predict. The world has moved on. It's a Damon mess. Good luck.