Take the 1 or the 9 to Van Cortlandt Park and Broadway, and then the bus up hill. I believe Metro North's Hudson Line (which stops at Spuyten Duyvill), should still be operating, unless anyone else here has any news.
Funny you should mention Riverdale as that's where I currently reside. I was in NJ today and decided I would be clever and take the Tappan Zee even though it was 20 miles out of the way from where I was. Well, wouldn't you know it everyone else did the same thing and it took me 2 hours to get home when it should have been 20 minutes. The kicker is the traffic reports were saying it was a 5 minute delay on the lower lever of the GW. Unbelievable.