If you are just using heroku to run a process it is pretty easy to rebuild on AWS. Here is one fairly solid guide: http://blog.clearbit.com/ec2-heroku/
Depending on what language you are using google's app engine could be a quick replacement.
Please do not trivialize the aspects of running a server on AWS (or a highly-available cluster) just for your own single application. Installing is the easy part, the day to day maintenance, reacting to issues, the 3am alerts (you set up alerting, right?) is what's costly.
I guess I was responding to the parent with ideas and links to use 'in case of emergency'. It isn't trivial, but some of these tools in conjunction with AWS make it possible to do alone, which I think is pretty cool. Alerting? Cloudwatch + PagerDuty gets me somewhat there.
Heroku is a great product and it going down permanently would be a huge loss to the community.
However there are a number of open source alternatives with very similar user experiences that you can run yourself in a variety of environments including:
From what kind of scale would you consider running flynn (I'm a fan since the early days) or deis (scoped it as well) a pragmatic step compared to heroku?
Depending on what language you are using google's app engine could be a quick replacement.
http://rogerstringer.com/2015/05/13/make-your-own-heroku/
https://github.com/buttfoundry-community/bosh-buttfoundry/bl...
Another HN thread: https://news.ycombinator.com/item?id=4183634
I'm not a big fan of docker for a few irrelevant reasons but using it w/ heroku makes it very easy to migrate to other container hosts.
edit: the founder of Flynn replied to parent as well, that is also a great alternative that I forgot to include.