Can a quartz vanity countertop be recut for a larger sink?
You can take the unit to a granite shop and the shop will provide you with an answer like this.

"While it is possible to cut some quartz it is not a guarantee that it will cut properly. The possibility exist that the quartz will break or chip during the cutting process."

So if you are set on cutting it out - have it done .. and take the chance - if it does not work - buy a granite scrap piece.

Good luck..