No, they wouldn't be fine!! Plants that normally grow out of doors in temperate climates do not make successful long term houseplants. There is insufficient light (even south fagging windows do not duplicate direct sunlight), too constant a temperature and a lack of humidity. Plants like Hydrangea paniculata need to go through a winter chill/dormancy period to survive and reset their biological clocks. If deprived of this dormancy, the plants will decline and eventually die. Even florist's hydrangeas, greenhouse-grown and intended as a flowering indoor gift plants, are only very temporary indoor dwellers at best.

Either plant them outdoors or return. They just won't survive long term indoors.

I live in a similar climate..paniculatas are great..my issue is too much shade but 2 new ones in my one and only partly sunny spot look so cute..a pic I took a few weeks ago

Just wondering, how many plants did you get? Paniculatas can be grown in part shade of full shade as they tolerate sun the best of all hydrangeas. Are you sure you do not have room? Those two are also quite compact!

Put them in pretty planters and place them where they will do well. Those varieties won't get huge and will do well for a while in large planters. Never return a hydrangea :)