So don't put portals on the same channel, failover is not meant to be common so better to have cleaner channels than CCI within the mesh cluster.
Mesh point failover from one portal to a backup can take UP TO 40sec, it depends on scanning, channels in the reg domain, etc.
If the need is a more mobile mesh solution, aka points on vehicles moving around, that is not supported. We have a few other options (501, instant with mobile mesh, etc) but in terms of ArubaOS, it's not supported.
If you want you can share your use-case, but generally Aruba's mesh is meant to be for fixed infrastructure.