Is it possible for svt to go away on it's own ever in an adult. like could it only last a few years? or if it's caused by a thyroid issue, autonomic dysfunction, etc. if the other issue is fixed it could go away?

There is no known precipitating factor for SVT. Some conditions such as hyperthyroidism or POTS may cause similar symptoms as SVT so if you fix those conditions symptoms will resolve. Most people with supraventricular tachycardia don't need treatment. I do think spontaneous resolution may happen but I could not find a reliable literature source to tell you with certainty.

If the cause of SVT is appropriately treated, then it would not reoccur. It also could be treated medically and or surgically with cardiologist evaluation through your primary doctor what is best suited for you would be done.