You can't get the seller's address or telephone number unless they are a business seller, in which case their details will be on their listings.
The only outcome you could get through Ebay would be a refund if you opened a successful 'item not received' case.
Your best bet really is to message the seller via Ebay.
If they are not responding to Ebay messages due to illness, they are not going to respond to a letter or phone call either.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)