So, they sealed Long in the Ball of Lamentation, right? Y'know, the spell the Fist Demons used against the Kensei, right? The one that has No Ontological Inertia and disappeared when Maku went kablooey, right? That means when the last primary-colored Gekiranger dies of old age someday, the most evil, badass mofo of all will be back at full strength, as if none of his defeats ever happened, and really, really pissed. Right?
If memory serves, the Gekirangers said that they would ensure that the sealing technique would be passed down from teacher to student from then on, thus allowing for each successive generation to renew Long's seal and keep him trapped forever (theoretically).
This is addressed in the Go-Onger vs. Gekiranger team up where Long actually escapes only to be defeated rather swiftly be a team of recently trained users of Jyu Ken. It looks like as righteousness will always prevail.
It just bugs me in a "how could they do that?" way that not only do Rio and Mele die at the end, the teamup brings them back temporarily only to sends them to hell as punishment for their cheating death. I like a Bittersweet Ending now and again, but... dude!
This one was probably fixed as of the Legend War. Presumably they were brought back to life by the same outside force that resurrected the other dead heroes. This time it wouldn't have been cheating death since it wasn't their fault they came back to life, so they'd go back to heaven.
If witnessing his mother's death in Long's hands caused Jan to forget all about his past and end up Raised by Tigers, how exactly does he know his last name?
Likewise, due to being Raised By Tigers And Pandas, how is he even proficient at all in speaking Japanese? I thought at least he'd have some episodes where he Hulk Speak all the way until someone taught him how to speak Japanese...
While the subs don't do a good job of conveying it, Jan's vocabulary and grammar are on par with a small child, with his made-up words sounding like baby talk. Amnesia can easily wipe out details about your own life while leaving skills, like language, untouched. Also, just because he remembers his last name doesn't mean he remembers why it is significant or important beyond it just being his name.