It is my understanding that the character sheet will remain, you just won't be able to make any changes to it. Also, when you duplicate a campaign, you must choose a sheet for it, so you probably won't be able to copy the campaign afterward. If this is your goal, make a campaign with a character sheet just-so, and make some duplicates for emergencies before letting your subscription lapse. The biggest danger in doing this is that any changes Roll20 may make in the future may require tweaks to your code to keep its functionality. The simpler the sheet, the smaller the likelihood, so that might be a design goal.