How much alcohol remains in strawberries soaked in alcohol?
I don't think this has a single answer: The amount of alcohol would depend on the alcohol content of  the soaking liquor or liqueur, soaking time, temperature of chocolate, and how thick the strawberry was.  

I suspect uncut strawberries would take at least several days to fully absorb alcohol and reach equilibrium, but the surface should take up alcohol fairly quickly. If they are cut up, exposing the more porous interior, I imagine an overnight soak would be sufficient to reach maximum alcohol content.  The enormous, bloated mutant strawberries you sometimes see at stores could take considerably longer than others to absorb their maximum alcohol. 

Alcohol is much more volatile than water, so the immersion in warm, melted chocolate would remove some alcohol, but once the chocolate cools, it should trap any remaining content.

The flavor of alcohol is easily masked by other flavors at under 20% content; this could explain why your friend didn't taste it, but you did.  It's quite possible the strawberries packed a sobriety-busting punch, but it was disguised by the chocolate and fruit tastes.