It's not like that chain was securely attached
Considering a queen xenomorph can ride the exterior of a spacecraft through a 30 megaton nuclear explosion & the vacuum of space, or live thru being frozen for 100 years at time for uncounted thousands of years, little seems as assured as the idea this particular queen would've been permanently trapped by her chain being jerry-rigged to a sinking tank, which only should've worked as long as gravity was pulling against it, but as soon as they both came to rest at the bottom, all she had to do was undo what Alexa did.
I suppose the argument could be made that being submerged in extremely cold water somehow put her back to sleep (though space is certainly colder & less oxygen rich), but esp with the warming of the poles, they have the potential for a sequel which should've been the natural follow-up to AvP instead of whatever Requiem was supposed to be. They could bring back Arnold, Danny Glover & Ms Lathan to lead the charge.