The phrase "abruptly so" is correct and usable in written English.
It can be used to indicate that something happens suddenly or unexpectedly, often in relation to a previous statement or situation.
Example: "The meeting ended abruptly so, leaving everyone confused about the next steps."
Alternatives: "suddenly so" or "unexpectedly so".
For us, things can change so abruptly, so violently, so profoundly….
"The movie had ended too abruptly, so what we did was flesh out the ending and add some more scenes.
When the music, played in the pit by Diane Pettipaw, Kevin Galie and Marina Gendel, stops abruptly, so does the dance.
She threw her arms around him to kiss him, but he turned his head abruptly so that her mouth landed on his ear.
There's frequent rain and the weather can change abruptly, so bring a windproof and rainproof jacket, warm socks, a swimming costume and powerful sunscreen.
But, after showing his parents the transcript, Martoma continued, he had to leave town abruptly, so he asked one of his younger brothers to compile the clerkship applications that he had left out in his bedroom.
Some residents headed to schools where classes were abruptly stopped so that the buildings could accommodate fleeing families.
But the halcyon days ended abruptly, or so it seemed, in the wake of the Irish banking crash of 2008.
At the same time housing market pathfinder funding has been abruptly halted so that in some areas contractual obligations for 2010/11 are problematic.
An opposition media group claimed rebel fighters Otaiba in Damascus suburbs feared a chemical attack after government forces withdrew abruptly and so donned gas masks.
For something catastrophic or even detectable to occur, the fault must abruptly get so much weaker that it can no longer cope with the stress by simply plodding along.
