Nodes that went offline for a long period of time are called zombie nodes.
What I imagine how my peer's node feels, when I have to force close a channel
The community or industry standard is to wait about 2 weeks to allow the node operator fix their setup. It's possible that they are moving, or their equipment failed and needs replacement. They may not actively monitor their node, and they may have not realized that it's offline. If you can reach out to them because you know their contacts you can ask them about the situation.
If all the funds are on their side, you should not worry about it. You gain nothing by closing such a channel.
Once the 2 weeks have passed and you have no way of reaching them, you may decide to force close the channel. Be prepared to wait a certain amount of time because the LN protocol gives the other party time to dispute your closing transaction in case you're submitting a prior state of the channel where you had more funds in the channel. After this time passed you will see the channel closed and your funds returned to your on-chain BTC wallet.
