In all payment-channel systems, including LN, the recipient has to be online to receive a payment. AFAIK the only way to receive a payment while offline would be to have someone else accept the payment on your behalf, absolutely trusting them with the BTC, at least until they can forward it to you. For this reason, LN isn't great for forum transactions, where you usually can't expect the recipient to be online.
Didn't know that. It's rather disappointing... I thought that the transaction would be on hold until either you receive it by going online or the sender closes it.
In any case, how about having a "bitcointalk.org" hub in which people deposit their donations and then you can redeem them into your channel in the forum by login in your account or something... kind of centralized but since it would be small amounts donated it wouldn't be that big of a deal, also there wouldn't be no KYC stuff involved. Im sure there is a cool way to implement this in the forum software in the future.