One problem you may have with dsl is that your local telephone company might not want to sell it to you without phone service. If they will provide it, you'll most likely also be charged for what they call a "dry line." It was $10 a month here in New York before Verizon stopped offering it.
Call your local business office to find out what the possibilities are.
Either way, you can't use an Obihai device without an internet connection, and bear in mind that GV won't give you 911 service. So, based on your situation, I'd say you probably want to keep your current service, and use the GV as an auxiliary line. You'll be able to save money by not having to pay for outgoing calls, which will reduce your phone bill, but unless you buy an ObiLine (FXO bridge device), you're going to need two wired phones, one for each line.
Good luck with whatever you decide.