Senders will keep mail for you in the queue only for a limited time, after a few days (IIRC) your mail will bounce. So if your host or ISP unfairly takes down your SMTP server and you have to go to court with them, you WILL lose mail.
Generally, running an SMTP server is quite a responsibility: not losing mail, not being exploited to send spam. What matters is not so much that you can set up in a few hours, but whether you want to take on that responsibility.
What? No. You just get another host somewhere (free amazon micro EC2, etc...) and point your DNS to that via your registrar. The only thing that can prevent mail service with longer than ~24 hours latency is a seizure of the domain.
Generally, running an SMTP server is quite a responsibility: not losing mail, not being exploited to send spam. What matters is not so much that you can set up in a few hours, but whether you want to take on that responsibility.