Unless the flow switch is in a place that would require the glue to be put on it, I would leave it in. If you will end up with glue on the flow switch without removal, I would take it out.
As for the hose clamp, yes, leave it on.

Hope it works out for you. Will be a cheap temp fix with very little labor involved so even if it doesn't work, the worst case scenario would be that you have to replace the collar anyway.

Let me know how it turns out.