A lot depends on how big a merc unit you are, and how deep your pockets are. I'd personally want to keep it, but...
Bearing in mind I don't have the sourcebook yet, and therefore can only go from what I've seen in the computer game, one problem you're going to have is spare parts: the Argo is essentially a unique DropShip, which shares spare parts with no other DropShip in the Inner Sphere. The closest comparison in size is the Behemoth, and I don't think they both use the Sunburst M-200L Megadrive drive system - the game gives the impression a repaired Argo can manage 4/6. Is that actually the case? If not, and it's really only a 2/3 or 3/5 ship, then that does open up the possibility of using the Behemoth's drive system as an alternative source of parts.
In terms of dupicating its capabilities, I'm not so much worried about the docking collar linking technology, either: it's essentially a breakthrough idea that failed to actually work, and doesn't really give you any significant benefits. What's a huge deal for the Argo are the grav decks, which no other DropShip in the canon have.
As for another power taking it from you, if it's really as much a civilian exploration DropShip as the fluff I've seen so far indicates, I don't know that there's really any danger of that. The Star League failed to capitalize on its revolutionary technology, like the Mammoth or Behemoth it's basically a civilian ship, and while it's purported to have better repair and refit facilities than other military ships, are they really that much better, or are they better than what your typical merc has in a Leopard class?
I suspect that most large military outfits would be better served by a Union or Overlord, which is better able to deploy the 'Mechs it carries, something an Argo would struggle to do, and both of which could, unlike the Argo, support 'Mechs in the field, on the ground, rather than requiring a second DropShip to load them up and fly them up to the Argo to unload them in microgravity for repair aboard the bigger DropShip.
With that said, there are two groups who, in the era the Argo was found, would really benefit from its features: ComStar's Explorer Corps, and Interstellar Expeditions. Their mission profile allows the Argo to actually do what it was designed to do, and serve as a mobile command post and field base for exploratory expeditions. Since that's well inside my own cup of tea, I'd probably keep it and go Lostech prospecting, but for most merc units, it's not as practical a ship, and they may be better off selling it.
honestly i'm surprised Comstar didn't pull a Vandenberg White Wings on the Argo.
There's really not that much advanced tech on there that tips the balance of power in the Inner Sphere or Periphery. I still question whether its repair and refit facilities are really that much superior to an Overlord or similar ship, its unique docking collar chaining feature appears to be a dead-end curiosity rather than a major breakthrough, and its other unique feature, grav decks on a DropShip, aren't earth-shattering in their utility either.