Warning: Spoilers for Episode 2 are in this article, You been warned!
Honestly, this is a fool thought that Aku has won just yet. Even watching Episode 2 and he stating he did in fact eliminated all the portals I can’t believe outright. Samurai Jack gonna get back to the past… If Aku “clearly” says he made way to eliminated all the paths home.
Starting with this:
The scientists Jack helped escape to outer space to a new home… the planet might be spectating and planning ways to help Jack further… since 50 years has passed they do know ways of time travel, therefore, they can go and help Jack. Its Highly possible they will return with some elite soldiers bots or people to return to send Jack to the past (Hoping for multiverse theory not to make a mess of things).
Destiny Portal that had the Morpheus-like character guarding it… the portal clearly is self-aware and we do now he posed to use that portal on the clear hints it makes. The Portal could hide or move, therefore, can keep Aku thinking he blew it up and it’s no longer running.
Monks that cared Jack’s Aku infliction… when Aku was sick and went home… Jack got infected by Aku… he had to be purified by the Monks of the mountain and they did state they could rebuild the portal.
Alternative Choice, Eliminate Future Aku then get back home.
Portals are not the only way Jack can return to the past. Aku death in the future could do a major blow to him in the past or open a portal back. With Aku dead in the future, there is only a short period where Jack’s Allies and friends will get him back. So if the works on attacking future Aku when he thinks he doesn’t have the sword anymore (and he recovers it.) Jack has been a Solo Act most of the time and needs a force to push Aku in a corner. This way if Aku runs… he is dead… if he fights he is dead.