CFS has plans for swappable vacuum chambers (1 year lifespan) and the liquid blanket will protect the magnets for a 10 year lifespan.

This talk by the MIT Nuclear Science department head explains the whole rationale behind ARC/SPARC, and this timestamp is where he starts talking about maintenance and the neutron blanket (5 minutes later): https://www.youtube.com/watch?v=KkpqA8yG9T4&t=2400s