I havent bothered reading this all but please excuse me if this has been covered.
NO tax or NO MOT will NOT void your insurance.
Under EU rules any car can be insured third party regardless of its condition.
YES you will be fined for no MOT and no tax but you are still insured.
I know this because I got stopped when my MOT expired the day before (i did book it in for 2 days time) and the copper left me off, and told me to drive it home, I said am I legal to drive, he said yes as I am insured.
coppers tend to clamp down on those with no insurance and if you explain yor situation you may be OK.
Its another reason why you see so many UK cars abroad with no tax or MOT but valid insurance.....they are legally allowed to drive said car overseas*
*there is a time limit though when the car is in said country.