The Withers Trial (idk what to call it)

A new quest of some sort where a sickness comes to ravage the land after you defeat the wither because its sickness spread. This can be optional i guess. Like you activate it with a mode like adventure mode. It can either hurt the trees (make then sick or decay perhaps) or the animals or cause fires or spawn more mobs or even open a door (at where you killed the wither) to the nether where fire and wither skeletons can get through. The only way to close it maybe could be by lighting a beacon or something like that at the source. Idk it just sounds like a cool adventure that you could even get an achievement for completing i guess.