For frontier Tribunals, the players are the only presence of the Order in the area. In Novgorod, the other mages might just be too far from the epicentre to be contacted in time or for them to care.
In general, the Order may or may not react to threats depending on whether it's individual members perceive it as a threat to them personally, and even then, only as their lab schedule permits.
Yes, I understand that you have a problem with the faerie queen of Winter, but I don't see it as a threat to my Covenant or my Vis sources.
Add to that the fact that the members might just deny that there is a threat (cf current antivxx/covid movement).
The rumours of a demonic plague of undeath are just made up by the Flambeau to justify interfering with the mundane and with the Oak Gild who wants to maintain control of the Rhine.
If the threat is absolutely real, plain for all to see and a threat to the very existence of the Order, a letter can be sent to your Quaesitor, who will inform the Praeco, who might bring it up to Tribunal. Then it might be selected as one of the three issues your Tribunal submits to Grand Tribunal (if the quarrel of a local archmage over a trespass by a mage from Provence 35 years ago can be moved down the order of business). And then concerted measures might be discussed: the next 7 years will be used to decide what leather, vellum and which ink to use for the books in which the reports of the findings of the committee on the evaluation of said threat will be reported back to Grand Tribunal, as well as confirming that Carolingian miniatures is the preferred style of writing for official documents. (the right answer being of course light brown ox leather, lamb's vellum and gallnut, but this needs to be established, should the brown be closer to walnut or hazelnut is the contentious issue).
You can portray the Order as utterly inefficient and mired in personal rivalries which prevent meaningful cooperation (much like modern day academia) or you could just have an organised gang of Tremere/ a brotherhood of Flambeau come and just solve the issue within 2 seasons of the letter to Coeris/Castra Solis being dispatched.
As a story teller, I would not throw such a danger at my party, because then they will quickly become spectators as powerful mages just come and solve the problem for them.