I second selling it. I've been surprised what a random website might get on Flippa, and Notifo has some recognition and cache. Might as well see if it can hit a reserve price - passing the service on at whatever price is probably good for the founders and users.
There is a similar type thing at www.notify.io which existed before notifio was around anyway.
it is still around. just using it today to prototype webhooks with openstack
Here are the bad news: it's also owned by another twilio employee and the single person behind it doesn't listen to the community, nor cares about it.