From what I’ve seen, it very much depends upon the attraction. In some cases a CM may attempt “to hold your place in line”, meaning that you will be escorted back to re-enter the queue where you exited it. If you were nearly at the front, you may be permitted to enter the LL. CMs do have the ability to issue ad hoc LL return times but apparently this is very much discouraged, and monitored, and CMs who issue too many are subject to discipline. And this case-by-case approach really isn’t something that’s brand new. CMs have always been empowered to come up with a fair and reasonable solution when things happen, like when a 5-year old child has a potty emergency right before boarding Peter Pan after waiting in line for an hour, and Disney’s expectation is that leave-the-line emergencies that have previously been addressed by issuing
DAS “just in case” can also be accommodated in this manner.