Why you think you will have a problem ? As long as you prepared to pay for Laos visa you are fine. For the Non O at Thai Consulate it should be OK. Your Non O is based on what ?
as this will become another complain topic about the Royal Thai Embassy Vientiane I will close comments. I send them a message asking to issue an Official Announcement about their policy so people not waste time and money.
After the stamp has been voided you can go out at Myanmar border or at Ban Laem or Ban Pakkard border. Avoid Poi Pet. You can also use a border run company to make the day smooth.