For how long has a channel been inactive? I would like to close channels for which there is enough evidence that the remote node disappeared and won't come back.
So my idea was to check for how long a channel has been inactive, and if it is > two months to close that channel.

How could I find out for how long a channel has been inactive (in LND)? Finding out which channels are inactive is easy by queryinglncli listchannels --inactive_only, but the result does not show any indicator about how long that channel has been inactive.
You can look for "last_update" field in getchaninfo output.

Below I also submitted https://github.com/edouardparis/lntop console screenshot which does the same thing.