Contacting advisor after long hiatus
I've been in a similar situation, and these are the things I took into consideration:


is it feasible to work on your thesis from abroad? Labwork would make that a lot harder, whereas computer simulations can also be done on a beach in Hawai.
do you have enough progress to finish the thesis rather independently? If so, I would try to write everything up and get it over with. 
How easy is it to change advisors? I know it is possible at my institution, but not easy to get done due to the paperwork and the different boards involved. Plus, it often means a change in subject so you basically have to start all over again. Is it worth the effort?


My gut feeling tells me you best just put some elbow grease on, devote some time to your thesis and wrap it up. Take it from somebody who spent three years struggling to finish a thesis due to work: you want to get it over with so you can move on.

So what I would do, is:


write up a bit more, so you add some beef to your work.
roughly plan the rest of your work: when will the results be written out, when will the discussion be written out, still simulations to do? etc. 
send an e-mail to your advisor explaining briefly that you had little time to work on the thesis due to personal reasons the past six months, but you want to finish the work in a timely manner. In a next paragraph, explain briefly where you're at now. Make sure to include briefly what you've done since you last contacted him. In a third paragraph, briefly give your planning and ask him whether he can agree on the feasibility of the planning.


You have to keep in mind:


supervisors often have more students. So big chance your supervisor doesn't remember the details of your thesis any more. That's why the brief summary is important.
supervisors like to see results. So if you show them effort, they often get more engaged in the discussion. A little initiative can go a long way, and showing initiative in your first contact mail is likely to get his attention.
a supervisors mailbox can get well over hundred emails in a day. They have little time, so keep it short. "Briefly" is the most important word in my answer ;-)


It might be possible that your mail get snowed under in your supervisor's mailbox. So if he didn't answer after a week, a gentle reminder mail -including the original information so he doesn't have to dive into his mailbox to find it - can do wonders.

Good luck with it!