I don't think there's any way of releasing the license without restarting the IDE's python process.
That said... I use an IDE called PyScripter which has a remote debugger. This means it can be restarted (or crashed...) without restarting (or crashing...) the entire IDE. To restart the remote python process and release a license after running an ArcPy script, right click the python interpreter section of the IDE and select Python Engine->Reinitialize Python Engine. See attached screenshot. Or hit Ctrl+F2.