There's no way to restore a connection broken in this manner (other than closing and re-opening the file) I'm aware of.
You could also go into the File>Manage External Data Sources, and manually repoint the path to the hosted file, but that actually takes longer than closing and reopening the local file.
And it will still fail if the served file is off-line when you attempt it. There is no way to "script" it, so you risk making a mistake each time if you re-set the path.
I've never had this problem with a Separation Model system, but I don't use local files as part of the separation; it's all hosted or all local.
This would seem a problem in Separation model solutions as well
The Separation model does not require the UI file to be local. It can be hosted. Probably should be unless you have such huge performance problems that requires the UI file to be local...
FWIW, I put in a feature request
This would also help with a solution hosted on more than one server, with no local file
And since one of the benefits of the Separation Model is being able to just update the UI file and upload it to replace the older one (without affecting the data file) using it locally would require replacing it on all devices. Ouch!