Vanyel is pretty sure Leareth and Nayoki discussed some kind of contingency for this but his mind is blank with surprise and shock. 

He relays Leareth's warning to everyone else in the warehouse, for lack of other ideas. :Brightstar can you -: 

Now that he has reason to look, Brightstar can in fact detect the six point-sources of magic, fifty miles or so away, and sends wordless confirmation. 

The contingency plan for if Thanos had time travel as well and could track them - or just made a correct inference about what they'd be doing and when they'd be visiting - was "get the hell out as fast as possible."

:Tony we're getting out: Nayoki barks to him, and reaches for the controls on her suit, to return to the Avengers' tower of the present day. 

Nothing happens. Thanos is blocking all time travel in or out within a hundred-mile radius of himself.

Tony throws the spare suit at Featherfire and taps frantically at the controls of his own suit.

"Fuck."

He tries a few more times, just to make sure.

"We should have thought of this—he has the Time Stone, of course he can block us from traveling—"

He radios Cap and Strange. "There's a situation. Thanos is here. Stopping us from leaving. Let's regroup at Cap's location—uh, wizards, you got that, right—?"

"Got it," says Strange via the radio, then Mindspeaks Leareth and the Ancient One. :We're regrouping at the spot where we came in,: he says, and opens the portal.

Leareth acknowledges this wordlessly and follows Strange.

It's less that he didn't think of this possibility, and more that it's not really clear what to do other than 'if you can't run, fight.' He went back and forth with Tony on the wisdom of a contingency plan that involved gathering all of them in one place versus dispersing; he's not entirely convinced the former is a good idea, but the latter isn't a great plan either. 

Nayoki is starting to get a bit winded from all the Gates. :Brightstar, can you -: 

Brightstar needs doors to use as Gate-thresholds, he can't do them on thin air (and until recently didn't know anyone could do that). The warehouse has a door though, and so do lots of the buildings where they landed, and he can do that from memory. Though the first try doesn't work because apparently the door he's anchoring on got blown up or collapsed in the interim. 

Within eight seconds or so there's a Gate up. 

Vanyel, as the most powerful and best at shielding himself, crosses first and scans the surroundings. 

There's nothing hostile nearby, except Thanos, who's still at Stark Tower.

"What happened?"

"We got Mind and Space to 2018. Then Thanos showed up—our Thanos, with all the Stones. He's blocking time travel out, somehow."

"We have our own Time Stone. Maybe we can get out with that."

He gestures wordlessly to the Ancient One.

She attempts to use her Time Stone to cancel the blocking effect in their immediate vicinity.

Green lightning arcs across the city from her Stone to the one in Thanos' gauntlet.

A moment later, Thanos is there.

"You fools," he says. "Thinking you could undo my great work. I am inevitable."

The arc of green lightning continues and intensifies.

The Ancient One is struggling.

:Help me,: she says to all the mages. :I can't channel enough power alone.:

Strange takes her hand and helps her.

:Vanyel?: 

:This place doesn't have nodes -: 

Leareth makes an impatient mental gesture at the Time Stone.

...That is not a node. If a node were a puddle after a rainstorm, that would be the ocean. 

It's probably not even the stupidest thing he's ever done. 

Vanyel reaches out to take Leareth's hand, both physically and mentally, slipping into rapport as Leareth joins with Strange. He reaches for the stone. 

- it hurts a LOT - 

He rides the wave. Stays in control, barely, and adds ten time the channeling-capacity of an ordinary Velgarth Adept to the mix. 

Leareth, for all his millennia of practice, isn't sure he would be able to do this at all, let alone with any level of safety, if Vanyel weren't there in mind-rapport with him. 

He adds his strength as well. 

REVEEEEEEEEEEEEENGE!!!!!! 

Brightstar has neither the Gift strength nor the training that he would really need to do this, but he's more than angry enough to make up for it. 

....Nayoki, on reflection, is going to stay out of this one. She has a suspicion that if this lasts more than ten seconds, very soon there are going to be three unconscious mages on the ground, and someone needs to be capable of dealing with whatever happens next.