Garfield is hallucinating, freezing and slowly starving to death.

So Jim Davis says this was just for the Halloween of 89. 

We take great pleasures in the tragedies. We adore pain in others. Jim Davis is just one such man. You got tired of drawing Jon's misadventures with Garfield didn't you, Mr. Davis. You just felt like causing him pain, indescribable pain, pain to the extent that you ret-conned more than a decade's worth of back-story and contradicting strips to come and with one strip everything about the orange fur-ball collapses into that one week you went crazy and killed Garfield. Slowly. Over decades. You let us watch his hallucinations, starve and die...for decades. You twisted human being.

Garfield was meant to face the truth his fear in this strip. He is alone. Waiting for Jon and Odie. But they aren't coming.

Maybe it was a Sunday.