I would refuse delivery. Quite simply, if you stick to your original story with ebay, regarding the 'item not as described'. Mention nothing to them about your removing the anti virus etc, it just complicates things. They will refund your money (which they are holding in escrow right now) and it will be the sellers responsibility to track/find his machine. Just be sure to include the tracking information in the resolution center case, and update it with any new information (by means of sending him messages exclusively through the case/resolution center). Send a message now asking why he's refused collection.
And anyway, if you sent it recorded and he's refused collection, will it not be stored at his local depot for collection, for a certain period?.
Either way. Message him, asking why he's refused delivery, through the resolution center case. Then contact ebay, or escalate the issue within the resolution center if you have the option. You have absolutely nothing to fear, the chances of them finding in favor of the seller in an 'item not as described' case is so remote it's not even worth worrying about. Genuinely.
Just to be clear here. Make sure you have your **** in order. You need to have a record of dates, tracking number(s), and to be sure not to say anything remotely blame worthy in the communications you have with the seller. The person who makes the decision, at ebay/paypal will glance at the resolution center information/messages, run the tracking number, and make a decision, quick as that. And there's no going back after that. So be sure to reference your communications with the guy, and most importantly!, the fact that the item was NOT as described, when contacting ebay/paypal on the telephone. The fact that ebay already sided with you and asked you to return it means it's game over for the seller; he's just buying time for some reason by refusing the item. it doesn't matter. You sent it, it arrived at his address, and was turned away, ebay will see it as his job to correct that. Just be very clear with them, when you call, and in your communications with the seller, that the item was NOT as described (mention it in every message).
Remember, it's not about being polite at this point. It's about getting your money back. So you state the facts in black and white in every message, and you take a slight accusatory tone, if needed.. There will be either an Indian guy or an Irish guy reading this in a few days and making a judgement. You're communicating with them by proxy of the seller now! (if that makes any sense)..