If you're relying heavily on Bootstrap templates and you don't want to migrate the templates so as to use MudBlazor components, I'd recommend that you stay away from MudBlazor altogether and use Blazor Bootstrap or a similar library. The templates would need in-depth modifications due to the differences in HTML/CSS/JS usage between the libraries, by which point it would probably be more effective to create your own templates from scratch.

As an additional side note, I'd strongly recommend that you don't start mixing different UI libraries. I've tried it with multiple projects, and it leads to an inconsistent UI and a hard-to-manage front end.