There's a possibility I might get offered a long term position for this fall. Don't know the dates yet. However, I already have 18 days scheduled with different teachers between now and winter break. I've done two long terms before, but that was years ago. I think may have cancelled a couple of jobs that overlapped with the long term, but I didn't get booked ahead as much then. I'm trying to decide what I would do it I was offered the long term. Should I cancel with the teachers for the dates that overlap with it? Should I offere to go ahead and do the jobs if the teacher cannot find another substitute? I'm really not sure what the principal at the school with the long term would expect me to do. Of course, there is the possibility that some of the teachers I am booked for would have adequate time to secure a new sub if I cancelled on them. What is your opinion?
Pretty sure that what the principal is going to expect is for you to be there every day. As soon as you know you have the long-term placement, I'd cancel everything that overlaps. If the gig isn't for sure but there's a good chance of it, I'd consider canceling any dates close to the potential start just in case. If it doesn't work out, you might be able to replace those dates with other jobs later.
I'm not sure about your district, but sub jobs in my district are snatched up in a matter of seconds. Seriously. Cancel them and if you really feel bad, maybe email the teachers explaining the situation. They will understand; a long term sub job is a great opportunity for you!
I would accept any jobs during any time for now, up until the point you are absolutely sure that you have the long term gig. You have to protect yourself to make sure you can work, just in case things fall apart. Then as soon as you know you have the long term gig, you cancel everything else - don't feel bad, this is just how it is, the teachers will understand. They will be able to get subs.
I would definitely accept jobs for now until you're 100% sure what the dates are for the LTS, you can always go back and cancel the other jobs that interfere with the dates for the long term gig.