Clary's blood oath won't keep Shadowhunters from coming back, though it is going on a brief hiatus. Will Shadowhunters be renewed for Season 3? After Monday's winter finale, the show will return to Freeform for 10 more episodes in Season 2B, however, its future is uncertain past that point. The network hasn't made an announcement either way, but there is no reason for Downworlders to be worried just yet.
In the first half of Season 2, Shadowhunters took on City of Ashes and City of Glass from the Cassandra Clare novel series. The show has introduced new 'ships, sacrifices, and some questionable characters. When Freeform ultimately makes a decision to renew or cancel the series, who knows how many twists and turns will have occurred.
Freeform is losing Pretty Little Liars this year, RIP, and will likely hang on to Shadowhunters. With equal parts fantasy, YA drama, and mystery it fits into a different niche genre than Stitchers and Beyond, but will pair nicely with Cloak & Dagger, Freeform's upcoming series and first foray into the Marvel Universe. While the Shadowhunters ratings have dropped a bit since the show's original premiere in 2016, it still has an avid fan base, source material for days, and the support of the network — who upped their episode count from 13 episodes in Season 1 to 20 episodes in Season 2.
Honestly, the source material is the strongest argument for bringing Shadowhunters back year, after year, after year. Not only has Clare published six novels in the Mortal Instruments series, but she has other companion books and companion series that could expand Shadowhunters into an expanded empire that rivals the Arrow-verse. There are at least two potential spinoffs, or at least ways to play around with the timeline, available to Freeform.
The Infernal Devices
This novel series is a prequel taking place in Victorian England. London's old-timey Downworld is not quite like modern day New York, but the Shadowhunter adventures are just as compelling. Tessa is just as cool as Clary, and easily deserves her own series.
The Dark Artifices
This Mortal Instruments sequel trilogy is still being released, much like Game of Thrones. There's also Tales From The Shadowhunter Academy and The Bane Chronicles, two collections of short stories that also feature writing from Maureen Johnson, Sarah Rees Brennan, and Robin Wasserman as well as Clare.
Basically, Shadowhunters needs to be renewed for Season 3 so that all of this lush material can be adapted to the screen.