I do that a fair bit, and I'll reply to messages if I get any, when i get back (even if it's just to say thanks but no thanks).
It bugs the bejeezus out of me though when people wander off in the chat room. Not replying instantly to messages is fine, but if I'm chatting to someone, then surely be it's not too much of me to expect to be kept informed if you're wandering off to make the tea, feed the dog, wash the windows, perform CPR on your 90 year old mother, etc.
Yes, that last one has been used as an excuse before.
Always speak your mind, even if your voice trembles.