Is it safe to not see a dentist for an extended period of time?

Rarely. Stuff happens. Somebody trained should look in there once in awhile.
Not smart to do. It can actually be more costly to avoid the dentist. Active decay and periodontal disease can progress to expensive procedures and become irreversible to the point where you can lose the teeth and cause other problems in the body. What people rarely think about is that losing teeth also loses important functions of eating and talking also.
No. Poor dental hygeine is associated with increased risk of several diseases.