Sorely is used to emphasize that a feeling such as disappointment or need is very strong. I for one was sorely disappointed. He will be sorely missed.

Will be sorely missed Meaning?

When something happens or is felt sorely, it occurs in an intense way. If you sorely miss your best friend after he moves to Hong Kong, you miss him a whole lot.

Will be sorely missed or will sorely be missed?

extremely; very much: I was sorely tempted to say exactly what I thought of his offer. You'll be sorely missed by everyone here, and we wish you success in your new job.