ever coming back for the MOT and just continue renewing the insurance policy?
You'd still need to get the standard yearly Polish equivalent of the MOT, it's cheap though, I think it's around 100zl.
Your standard insurance policy will not cover you if you are living abroad. They'll only cover you if you're travelling on a holiday or business, but not if you have a permanent address. I know that in Ireland for example, insurance is cheaper outside of Dublin....so you can insure your car with an address at your parents house and live in Dublin, however, if you have a crash in Dublin they will want to know what you were doing there and they will go as far as to investigate whether you live/work there...if they find you do, they'll rip up your policy and laugh at your claim.
However, Polish insurance is a lot cheaper than in the UK.....over here you only insure the car, not the driver, so for example, when I started driving, a quote for me to be insured on a car in Ireland (where I'm from) was roughly 2000 Euro, same policy in Poland was 1400zl.....or 350 Euro.
It might be different for RHD, but you'd need to contact the people that ForFour wrote about.