这个句子哪怕是去掉next Monday,也是表示“与将来相反”.因为在if从句中用were to do结构就是表示和将来相反的用法.
虚拟语气中,在if从句中表示与将来相反的结构有：1) should + 动词原形；2）were to do；3）用动词的一般过去式.主句则用would/could/should/might + 动词原形.
eg：If there should be any questions,please contact me without hesitation.
He would not accept your idea if he were to come tomorrow.