Type 1 Advice when forgotten to reconnect pump

You are not alone. I have forgotten to reconnect an grateful I don't have that option since I went tubeless.*
Apart from getting into the habit of placing my pump on top of my pile of clothes before jumping in the shower, I didn't find a great way to stop this happening.
As for the protocol I adopted it was a bolus made up of
- the basal which I missed during the untethering
- the additional bolus I needed due to insulin resistance at high levels (when over 15, I need twice as much insulin as a correction)
Plus
- keeping a close eye on ketones
- frequent finger prick tests (CGMs are notoriously inaccurate at high levels)
- trying my best not to rage bolus because my levels were not falling fast enough
- a temporary bolus of 125% for 2 hours ... or until my levels were below 10

This is not the official guidelines; just what I followed for myself.

*I cannot temporarily disconnect my tubeless pump but I do change it after a shower and I can get distracted between the bathroom and my office where I keep my diabetes supplies. So, I have needed to follow a bit of the above on at least one occasion.