1 - if I have a LN channel open with the dealership, and the dealership does not offer intermediary services, then the only use of that LN channel is to transact with that dealership. If the dealership is connected to a LN hub that I am not connected to, then I cannot transaction with that LN hub without the cooperation of the dealership, or I would need to route payments via other means to that LN hub via other cooperating LN channels.
That's why I suggest opening a channel not with the dealership, but with a hub, in this case.
then the dealership would be able to claim the full $25,000 in the LN channel, however the tx fee would likely be greater than $10, so they are loosing money by doing this, and there is the potential that for whatever reason, the dealership does not realize that you broadcast an old closing transaction and/or the dealership is not able to claim the entire balance in the LN channel because of on-chain transaction backlogs, so there is no financial risk to you broadcasting an old transaction, because after tx fees, you would have gotten nothing after the channel is closed anyway.
If tx fees are so significant, the dealership, as well as other intermediaries should abstain from completely emptying balances of their counterparties in their respective channels. Always leave enough in a channel to cover possible onchain fees. Also if onchain fees are so high, it's an additional incentive to use LN.
Every LN participant and especially intermediaries, should be online often enough to check for old commitment txes, before their outputs become spendable for their counterparties. Transactions backlog may be a problem. But provided that enough funds are left in a channel, it should be possible to offer miners enough fee to get ahead of queue without suffering even a small loss. Also there are solutions proposed for fast dynamic blocksize:
https://bitcointalk.org/index.php?topic=1713807.0