I seriously doubt a brand would dump a player per se for having the branding of another company on the end of the bat handle. For instance, if a big brand ambassador like Kane Williamson did it, I don't imagine for a minute that his deal with GN would be terminated.
What it could do is give legitimate grounds for a brand to dump a player they no longer fancied paying, particularly in a cost cutting environment. The type of clause would be gets fairly water right even if the brand was utilising it opportunistically