The honest answer to that is "no." There is an ATM at the Thomas Bay, but it's about as reliable as the UK weather.
The next nearest are Avliotes and Arillas. Arillas is a less-punishing walk. I don't know how reliable the Arillas ATM is!
There are quite a few ATMs in Sidari.
Many places take pre-paid Euro cards for meals etc.
Personally I take mostly cash, including some GBPs, which can be changed at San Stephanos Travel is you run low on Euros.
As far as Greece staying the Euro goes - as far as I can see the EU will do as much as possible to keep Greece in, so I'd expect at least 8 weeks of to-and-fro after the election, so my guess is that things will carry as normal through the summer. I don't know if you agree, but it seems to me that the ultimate decision will be taken in Berlin and Paris, rather than Athens. Either way, I don't think the outcome will take years.
I agree with Waspman. The situation across the whole Eurozone is very unstable. All ATMs in Portugal stopped working for four days not long ago. Friends just back from Crete said they couldn't find a working ATM. So the sensible strategy is really to take cash. Ag Steph is generally a crime-free zone: it's not Sidari or Kavos.