If there has been no reply to the unpaid item case in 4 days, yes definitely close the case.
The buyer gets 4 days initially to pay and then a further 4 days in the unpaid case so 8 days is ample time to pay or the very least make contact.
Buyer gets a strike, you get your fee back and are free to relist.
Add the buyer to your BBL so they cannot do it again.
I only give a buyer the minimum time of around 8 days unless they contact me to make arrangements.
If they contact me they can have 4 weeks to pay, as long as I know where I stand, communication is the key.