Retrieve troops - bug of the game ;P

[shadowfax044]

If a village you had stationed troops at is razed or captured, those troops are lost. There's no way to retrieve them, unfortunately. But if the person wasn't your vassal, I'm assuming you stationed troops there to help that player protect their village, which means that your troops were likely killed during the attack that took the village, anyway.

[Redearthae]

In your make troops screen, bottom right hand side is a "i" icon in the reinforcing column. Click it, then there should be a retrieval on this screen