Yes. You can always go to 'My Jobs' click the name of the Job, click the '...' menu toward the top right, end the contract yourself. There used to be a 'reason' you could give for closing the contract that said something like 'client unresponsive', but they just recently changed all the screens around again, so I don't know if that 'reason' is still available.
IMHO. 3 months is way too long, especially if you never started any work for the client. Unless a client informs me up-front that the project/work will be delayed (until X date) after they issue the contract, I don't think I would wait more than a week or 2 without a valid explanation for the delay before closing the contract and moving on. I definitely wouldn't wait if they just aren't responding and aren't explaining anything at all. It sounds like the client is either playing games, did a hire without thinking it through completely, is truly unavailable/incapacitated and can't respond, locked out of their account, or simply lost interest in the project altogether and was too rude to tell you what was going on.
Your best bet is to close the contract out while the client is still 'ghosting', and chances are they won't notice the email they get saying the contract was ended and won't log back in to Upwork during the 14-day 'window' they have afterwards to leave a 'review'. You would think a client that 'ghosted' wouldn't leave a bad review about the freelancer, but you never know. Best to just close that contract out as 'quietly' as possible and let the 'ghosting' client vanish in the rear view mirror
