If you're re-starting church in your building this Sunday, can I make this plea to you? You have, as a church leadership, and in consultation with your church membership presumably, made the decision to do so. You've taken all necessary precautions, listened to the best advice you can find and have decided to go for it. God bless your efforts. But, please, if members of your church choose, in good conscience, not to return yet, please don't label them 'unfaithful Christians'.
Please go the extra mile not to put pressure on them to conform their conscience to the decision that you and others have made. It isn't a simple equation of 'the church is gathering physically so if you can do so but choose not to then you're sinning'. Of course, you have never suggested that was the case, but that impression can be communicated in so many small and subtle ways - so you need to be very intentional about making sure no such pressure is felt. Bend over backwards if necessary. They are not weaker brothers and sisters; they have simply made a different choice to you and they have liberty in the Lord to do so. Don't they?
After all, we shouldn't imagine that all those who do gather physically are there because they are, obviously, the faithful ones. Maybe they're there because, against their better judgement, they think they owe it to you as their pastor/elders to do so. Perhaps they're there in fear - not of the virus so much as the disapproval of their brothers and sisters. Fearful of how they will be labelled. Being there for those reasons is not a matter of faith but of fear of man - and you know how that gets described in the Bible.
Faithful Christians? It's not a matter of dividing along lines of who came and who didn't. Surely we know that, don't we? It's not about those who have disappointed you and those who have supported you, right? You're comfortable with liberty of conscience, for all God's people, aren't you?