If boss cancels your ARC, you’ll need to leave within 2-5 days. Both the work visa and the multiple entry visa are voided. You don’t need to hand in your ARC.
Options:
ask boss to hold off on cancelling the ARC for either 2 weeks-till May 16th, or for 6 weeks-till June 16th (for this 2nd option, maybe offer 5,000 as deal). If boss can delay for two weeks, then you’ll only need one quick trip combined with a landing visa.
fly to HK and get two month visitor visa…that would cover you. I am not sure about the situation regarding these, encourage you to surf forumosa.com a little more, and hopefully someone can give more advice.