I think the PriMapState() UDF can help you.
I presume your old printer server should still be running
PriMapState("\\OldServer\Printer1")
will return
1 if printer connected
2 if printer is default
nothing if not connected
I presume you can create a script enumerating all of your printers on the old server and if 1 or 2 is returned, remove it, install the one from the new server and if return was 2, make it default.