Answer: Fire blight, caused by the bacterium Erwinia amylovora and can infect cotoneaster, flowering crabapple, flowering pear, hawthorn, photinia, pyracantha and mountainash. Hibiscus is generally not affected by it. However, copper-based bactericides are used successfully to control the disease. I think, since you've already pruned out the affected plant parts, your hibiscus stands a pretty good chance of recovering. I'd allow it to regrow and see how it looks.
Anthracnose infected plants generally have a dark streak on the inside wood of cut branches, which makes looking for the streaks a good test in either confirming or ruling out the disease.
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