I would advise against it, to be honest. I can understand not wanting to stay in psych forever, but you'll kick yourself around the block if you don't accept the "dream job". And compounding the mistake by taking a med/surg-type position when you didn't enjoy it the first time around......why would you deliberately do this to yourself?
It's OK to be curious about other types of nursing jobs
. I've thought for years that I'd make a good hospice nurse, but I'm a DON in assisted living, and loving it for the most part. Recently, a brand new hospice facility opened up in my area which is much closer to home and the pay is probably equal to or slightly better than my current salary, but did I even consider it? Yeah....for about two seconds, and that's for a job I know I'd enjoy.
If I were in your place, I'd take the IP case manager position and forget about being "pigeon-holed". There's probably a darned good reason why you've stayed in psych......such as, you're really good
Do a 'gut check'---listen to what your instincts are telling you. Best of luck!