My recommendations:
When it tastes good, hit it with gelatin to remove ~90% of the yeast. Wait 48 hours, rack it off the gelatin and yeast, then add sorbate and Campden in the recommended amounts to slow down fermentation even more. These chemicals don't kill yeast but they injure the yeast pretty badly. From there you can add your backsweetening (if any), and keg or bottle as normal. If you're bottling, carefully monitor for carbonation by popping a bottle at least once a week, and as soon as you detect any fizz at all, chill all the bottles down immediately to prevent explosions. If kegging, no worries. In any case, keep it cold so it doesn't dry out again, because the yeast will in fact continue to work on it slowly for many months, even with sorbate and Campden in there.