It depends on how far either side is willing to go. The UK is one of the few countries with which the US has an annual trade surplus ($21.8bn),[1] which is worth a lot more each year than Giphy's purchase price or even Facebook's UK revenue, so there is a lot of room for retaliation.
Traditional British media will drum up support for anti-Facebook actions, and the current UK government was elected on a mandate of defending perceived British sovereignty, with economic considerations being less important.[2] The UK government has already engaged in actions that harm its economic interests to safeguard its sovereignty.[3]