I don't believe Amelius ascended as the Alteran people didn't discover how to ascend themselves until millions of years down the road from this point forward.
It was only the Alteran who existed within the past 10,000 who learned how to ascend.
it's also possible the Ori created their own gates based off of their existing tech that was left behind by the Alterans who left, i mean just because they took off within their ship doesn't mean no other tech existed after they left their entire galaxy.
Because after all they were once a space traveling society, but it's possible that the ring transporters already existed and because the transporter ring tech is related in how a stargate works that it's possible that Amelius only got the idea from this existing technology that helped inspire him to create the stargate technology.
this is sort of a side point, but just because one man learned how to create something into existence, doesn't mean that he's the only one to create that same invention on his own, especially if it's based off of existing technology. the man who created the bow and arrow may not be the only man who created their own version of the bow which has the same concepts only work slightly differently. meaning they could come to the same conclusion without even knowing or being anywhere near each other.
Anyway going back to the story....
Both factions of the Alteran people were once united as one people before some started to split and side with the religion of Origin.
This is a theory i have had for some time that i once brought up that didn't get a whole lot of traction because everyone just refers to the wiki blindly, but i think the wiki is incorrect because lack of information in the series at the end, so the wiki explains that the Ori didn't ascend until long after the Alteran left, without leaving examples of how the wiki came to this conclusion, (which didn't make much sense to me) but it's explained in the wiki the Alteran felt a need to leave because they were being outnumbered by the Ori followers, but the wiki also explains that the Ori followers didn't use technology at all.
Which doesn't make much sense in my opinion, because what would a highly technological advanced people have to fear from a primitive people who got rid of all their technology?
Not only that, but how would the followers of Origin even be a threat if this information was true?
I personally believe that the ascended Ori already existed, which the wiki explains they weren't, but i believe they existed in much fewer numbers within the ascended rankings at this point in time of their history.
It made much more sense that the reason why the more technological Alterans needed to leave in the first place was because the Ori were ascended and had an almost limitless power, you see the movie the Ark Of Truth only explains a small sliver of what the show writers had in mind to explain as they had a lot of information about the Alteran history they had to leave out of the movie to wrap everything up in the storyline, i read that they needed at least 2 full seasons to explain these details properly, which would have included 40 episodes that they needed to condense into a 1 to 2 hour movie.
This is why the ending felt incomplete and some things were just completely skipped over to end the story of the Ori.
So it's possible lots of information was planned out but because the show was cancelled, they were only able to release the movie to sum everything up the best they could.