The Secret of NIMH 2: Timmy to the Rescue
The building they are in catches fire during the fight.  The survivors (Timmy, Jenny, and her parents) flee. Timmy goes back to save Martin. Before he leaves, Jenny tells him she loves him and he tells her the same. Timmy and Martin are able to escape through the lab's skylight, with some help from Jeremy. Jeremy takes the survivors to safety. The mice return to Thorn Valley, Martin returns to normal and Timmy is now a hero. A likeness of him is added to the statue of Jonathan and the people of Thorn Valley cheer.