There are methods that are "easier to cover" as an accident. There are quite a few deaths that are recorded as "traffic accident" when it is a clear suicide, for example.
The only way I can see to emulate an accident with Sn is that you have previous knowledge of chemistry and your own equipment, so it could be an "accident" by inhalation in some experiment but still...
I don't like the "disappeared" option (my opinion), the doubt about your state that your parents would have could accompany them throughout their lives, especially if they cannot find you. I would leave a note somewhere where sooner or later they would find (or maybe send a letter the same day you disappear).