Is there a way to get some output back to the interface after executing a!startProcessLink(), or a way to update some variable inside the interface to insure process has been executed
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In general, nope - for such use cases you'd want to use a!startProcess(), or a Record Action configured to open in a Dialog.
(I've been campaigning for a long time to get "open in dialog" functionality added to the Start Process Link component, but it's in the "feature request backlog" dumpster / landfill, as far as I can tell. Which is sad because it would satisfy a lot of current corner cases.)