Ooooo...not a fun situation. When I loan my gear, I always make it clear to the borrower - and require their agreement in advance - they're responsible for repair or replacement of the mics in the event any damage occurs while the gear is in their possession.
I've always considered this an unwritten rule when borrowing products of any kind, whether it's recording gear, motorcycles, etc. But it really depends on the arrangement - if any - you have with the loaner of the gear, your personal perspective, the loaner's perspective, etc.