It sounds like the missions are still available for now, but I'm not sure for how much longer.
Edit: But you won't earn any permanent rewards for completing them anymore.
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It's official, Hurston Dynamics has emerged victorious in the Race for Stanton, securing their dominance in the Regen Crisis.
Thanks to everyone who rallied to help Stanton’s Big Four tackle the Regen Crisis following Imperator Addison’s call for scientific resources. Thousands of citizens have been hauling, mining, defending, and recovering lost cargo to support the cause, all while earning a wealth of rewards.
As of September 16, a staggering 337,131,104 SCU have been hauled in support of the mega-corporation Hurston Dynamics, crowning it the clear victor. Trailing behind, microTech has gathered 249,131,344 SCU, followed by Crusader with 205,035,536 SCU, and ArcCorp bringing up the rear at 193,710,144 SCU.

Rewards:
- In Alpha 4.3.1, players who have reached Tier 5 with the winning faction in their quest to assist the mega-corporation will receive an exclusive Strata "Hurston" Black Armor with the HD's logo.
- In a future update 4.3.2, Hurston Dynamics will also take over ownership of the Pyro Gateway space station in the Stanton system, with decorations and ownership visually represented on and in the jump point station. Additionally, all players will also receive a permanent 5% discount on all products, ships, items sold in Lorville's landing zone, low-orbit space station Everus Harbor, and also its newly acquired jump point station.
For more details, visit the official Race for Stanton page.
Ok, just got done with an Onyx facility, while I felt overrun at Lazarus, Onyx was challenging solo, but it wasn't like the enemies we're respawning every minute. I didn't time it well, but it felt like a 5 minute respawn timer. It was doable, and the parallax rifle is definitely my new favorite mid-range weapon.
I would recommend at least taking a nursa with you if you can carry one.