We definitely have no plans to change URLs. So as long as iNat is around, it is highly unlikely the URL would change, but we can’t make any 100% guarantees.
A few iNat staff members (including me) did some editing on this paper, which goes over a procedure to use iNat with herbarium specimens: https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/aps3.1193