I don't think anyone here is going to tell you its completely safe to buy any expired domain without an owner wanting it back since if you think about it many expired domains were formerly owned by some type of company, non-profit, for-profit, LLC, etc. Some forgot to renew, others didn't update their WHOIS and never got notified, some went out of business, some had multiple domains and let some go, etc. etc. As far as non-profit companies, I never lost one to a UDRP (only some for-profit companies), but buying a non-profit company domain is no guarantee they may try to file one. Usually what happens if a former owner wants it back is they will contact the WHOIS information (phone or e-mail), tell you some story about why they accidentally let the domain expire and either ask for it back or ask how you got it in the first place. I get those all the time. My response to them is Sorry I don't deal directly with former owners and if they are interested in a domain to please contact a domain Broker such as Godaddy to make an offer. The other option if you're parking it is to use a for sale banner, use DAN or other method. Remember that to file a UDRP against you is going to cost a former owner around $2,000 USD minimum with some legal help so you can always counter for less than that if you get approached by a broker. Usually I don't hear from them again.