Hi @Simon_H! Welcome back to the community. 
My general recommendation for use cases that are truly critical and that rely upon high availability is to use an external resource instead of relying on RetoolDB. The biggest reasons for that are redundancy, control, and customization.
That said, I'm fairly sure that stored procedures and functions are just as safe as typical table data. I'll reach out internally to confirm that and will let you know if I hear otherwise!