Apologise to the client for your casual attire and give the reason. Perhaps mention it to your boss when they come back.
To be honest, even if all my work clothes got destroyed today, I still have some dresses I could wear or skirts which I generally keep for outside of work but could be dressed down so that I still look office like. Do you honestly have nothing like that? Just jeans? Think about it for tomorrow, there's probaby something in your wardrobe that will do the job.
I'd also prepare for a bo110cking when boss gets back since they'll probably hear about it. Take it on the chin and apologise, I imagine it's unlikely they'll fire you for it.