as another experiment I have not taken my passport out of my drawer except for immigration visits, work permit, social department and opening my bank account last week for the past 3 years. Never needed it for traveling or anything, just use my licence.
A re-entry is valid for as long as the visa is valid.
With most education visas that means every 3 months you get a visa extension.
So that means your Visa is expiring every 3 months.
You can arrange to get your visa up to one month early.
That gives you 4 months to be away if it's a desperate situation and you want to keep your Visa before your next extension.
I am thinking that you're in your first or second visa extension, because if you're in your third visa extension you wouldn't be asking this question you would just leave early.
If you can get your next extension early you get around 4 months away with a re-entry to keep the visa. But actually you lose the class time usually. Unless you have a flexible Visa like Muay Thai where you can take extra classes to make up the time.
per capita Chiang Mai has more vegan restaurants and infrastructure than anywhere else in the world. Plus many bulk food supply options for bakery and grain supplies.
Almost everything is cheaper and more relaxed than BKK.
Plus a huge range of international people to meet.
there's plenty of ways to stay in Thailand long term and I live on $400 a month for the last 12 years. Feel free to contact me if you want to live in Chiang Mai. There is lots of things to keep you occupied and out of mischief.