If I took over the show from here, and next season had to be the last, here's what I'd do:

Gwyn gets his happy ending next episode and leaves the show. Matt Ryan ceases to be a series regular. Human Gideon sticks around and continues to be Gary's love interest. Evil Gideon is reprogrammed and turned good. It's hinted at that there may be some truth to the futures Evil Gideon showed the Legends. Booster Gold appears to warn the Legends of a future threat.

Next season is 15 episodes long. We learn more about Booster Gold's backstory, including that he is the father of Rip Hunter and founded the Time Masters. The future threat is the Thanagarian invasion, which Vandal Savage is indeed needed to stop. So Astra uses her connections in Hell to retrieve Savage, who is still the Jenga-loving goofball we saw in S4. Nth Metal is introduced, and the team all gain the ability to fly from it at one point. The Thanagarians want to make Earth into a slave planet. Onimar Synn is the season's main villain and is in charge of the Thanagarians. Rip Hunter and the Hawks (With better writing!) return over the course of the season and play major roles in the storyline. The former is from some time between S2 and S3, but the latter are from the present and it's revealed that they've since settled down and started a family. At some point during the season, Sara and Ava leave the Legends and settle down and adopt their daughter. Eventually they rejoin the team. The final battle has the Legends pull every Legend that's ever been on the show (barring characters whose actors refuse to return or are unable to join production due to Covid restrictions) from time to fight alongside them in a big, Endgame-style showdown, culminating in Sara sacrificing herself to kill Synn and free the Thanagarians from his control. The Legends all retire, with Booster Gold being given the Waverider. Ava founds a new generation of Time Masters and raises her daughter. Nate becomes an author and gets to keep Zari's totem, allowing him to visit OG Zari whenever he wants. Behrad marries Astra, and they have a son named John (after Constantine). Behrad also becomes the star of a Mr. Rogers-style show while Astra becomes President with Spooner as her Chief of Staff. Zari stays by her brother's side. Gary returns to his home planet with Human Gideon. Finally, Ava is eventually reunited with Sara in the afterlife similar to how Felicity was with Oliver, and we see that Sara was reunited with Laurel as well.