IMO, you should either bring the wires up into the new shed, or you should pull the wires back through the conduit and discard.

Here's why.

Over time water, bugs, rodents, etc. may cause any connections in that conduit to degrade. You might need power someday and it won't work, and trouble shooting later is much harder.

But also, sooner or later somebody will hit that conduit digging, and nobody will remember what it's for. If it has wires in it, they have to trace them and make sure they're not feeding an iron lung or something. If it's empty they can just drive on.

Really, leaving anything in the ground you don't need is a bad idea. You've already proved that - you don't know exactly where the end is, how deep it is, etc.