Fastoon was the ONLY Lombax Planet, while this wasn't confirmed, there has only been Lombax history in Polaris, and only one Lombax planet in Polaris… Fastoon!
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And yea he didn't even know about Ratchet 'till the attack on Kerwan (and most likely, an attack on whatever planet Angela was at too (as said by Kip Darling the last that was seen of Angela was her being saved by Tachyon's troops by Max Apogee).
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Perhaps he still can meet other Lombaxes… If he can reach thier dimention…
Well, I agree with the parts I left unquoted and the last - it would be silly to question confirmed facts or obvious things. But:
1. Why would the lombaxes stay just on one planet if they possessed such skills in engineering? Wouldn't others want to employ them to build machines of all sorts? And any people with that advanced tech would found trading outposts or colonies on other (uninhabited) planets too, like they did with the military facilities around Polaris. That's why I think they were spread around Polaris, while most of them were obviously living on Fastoon.
If Ratchet's, his father's, or Alister's personalities reflect anything of lombaxes in general, there must've been lombax adventurers and explorers who have travelled far, and some of them might have settled down on distant planets on distant galaxies, possibly even beyond Solana and Bogon (though we don't know if these are even near each other, but at this point I assume at least Solana lies near Polaris). They may have survived if they were lucky.
I didn't mean there would be a surviving lombax planet or something like that out there, but more of an outpost of several lombaxes who couldn't for any reason reach the Dimensionator (imagine even evacuating a single city through one portal, it would take ages). Or maybe just a few scattered around the nearby galaxies. But they've definitely built outposts, though they might have been destroyed by Tachyon.
2. Well, Tachyon probably knew Angela was a lombax as she and her origin was known in the news broadcast as well, but she might have just been an unknown rebel Tachyon wanted to get rid of and that would've been why she was chased. If she and Max would've last been seen near Jasindu, I would've investigated the whole planet immediately if I were Tachyon (but only if I would've known she indeed was a lombax), and possibly have found the Dimensionator.
3. That is if he finds a way to travel there. I'm actually quite surprised that never came to Alister's mind seeing there are other inter-dimensional devices, in as easily acquirable items as the Rift Inducer 5000. He though wanted to save the fallen lombaxes and return his honour, not just go to inform they could return home it seems.
From what I understood, Tachyon did a surprise attack on Fastoon, the Fastoonian lombaxes had barely any time to react, far from sending a message to other lombaxes in space or on other planets and waiting for them to arrive as reinforcements or to get to the portal. If they could've prepared for the attack, they wouldn't have fled. It all happened quickly, so I doubt all of the lombaxes were called to battle or to the Dimensionator portal, apart from reaching it. Though, the possible outposts could've been evacuated creating portals there too.
And if I were a lombax who heard of the attack but couldn't reach the portal, I would have tried to gather all of the others there were left together and either ambush and assassinate Tachyon as revenge or then flee to a distant god-forsaken place where we couldn't be found.
I'm sorry about how overly long this reply became, but I tried to make it as tight as possible.