Pug,
One of the first MPL courses at Sterling Airlines in Danemark went bankrupt before the MPL candidates finished line training, not sure but I believe those did get taken on by other 737 operators. Other than that to my knowledge covid is the first time the MPL to the partner Airline flow has been interupted, so this situation hasn't happened before where MPLs need to seek alternative employment away from the original partner airline; so what I say is from a regulatory perspective not what has necessariy happened in practice.
The Easyjet MPL had 70 hours of SEP time, however the latter part of that which is the introductory IF phase is still done as "pseudo" multi crew.