Hi there
I returned to work when DS was 6 months and he also refused the bottle, still does!
He does however use a sippy cup, but will not have EBM, it's boobie or nothing!
He has slowly started getting a lot better with his drinking but i found the only thing he would drink out of the sippy cup was rice milk and juice (he will not touch water not matter how persistent I am)
Rice milk apparently tastes similar to breast milk, and while it should not be used as a substitute feed, when you are as desperate as i was you'll try anything!
We also got around it by giving really milky custards and things like that.
Over the last week he has started taking cows milk from the cup much to my delight!
Everyone will tell you that they will survive without you but you'll never believe it until it actually happens, so yes, whilst it might be a stressful week or so, you'll find your own way just like we did.
In the mean time, keep trying the bottle or cup, you might just get lucky.
Good luck with it all, it will be fine!