Transmission not working properly

While driving the van started to slow down, then came a knocking noise and the van stopped moving. I gave the van a minute before I turned the engine back on and the van was moving but I can feel that it was still going a little slow but no knocking noise. The transmission fuel was a little under the line and there's a leak from the rear seal of the transmission. I got the transmission fuel topped off and the van is running fine as usual at the moment. I'm still going to proceed with having my mechanic take a look and figure out what needs to be done but he's not able to look at the van until the end of this month. I live in this van so there is usually a lot of driving throughout the day but I'm able to limit some of the driving. Just curious if you think the van can make it till the end of the month in this state or not. Thanks in advance.