It's a pity you didn't put this question to your doctor. S/he knows your medical history.
That said, prediabetes is a very individual disorder and so too is our reaction to medication. As you've only just started taking metformin tablets, it's too early to know how your body will react to the drug. The fact you're going on holiday next week adds further variables, which may not apply at home.
As I see it, your safest option would be to stop taking the tablets until you are home again. You've managed thus far without medication and another 7 days or so is not going to make much difference in the grand scheme of things. Meanwhile, I'd equip yourself with a meter and test strips, so you can keep an eye on your blood glucose levels at home and away, then compare your results once you resume metformin therapy.
Metformin is widely prescribed. I've been taking metformin daily for years and drink occasionally (most metformin users do), but not every night.. There is a small risk of developing a life-threatening condition termed lactic acidosis, as noted above.
Metformin seldom causes low blood sugar (known as hypoglycaemia or hypos for short) when taken on its own, but hypos can happen when you take metformin with alcohol.