Sorry about your mother.
RobsLuv and bobshynoswife are correct that you going to Canada will have no adverse effect on your application. And, if your husband returns to Thailand, it doesn't mean that he has to transfer his application to Singapore. If I remember correctly, you chose Beijing because your family has been living in Mongolia and hubby had been legally admitted for one year therefore meeting the requirements of choosing a different processing office than his home country. Him returning to Thailand doesn't change the fact that he met those requirements when you applied. The only part to be worried about if he returns to Thailand is if an interview is requested he must be able to travel to Beijing to attend. If that's not an issue, then you don't need to worry about the processing office.
RobsLuv and bobshynoswife are correct that you going to Canada will have no adverse effect on your application. And, if your husband returns to Thailand, it doesn't mean that he has to transfer his application to Singapore. If I remember correctly, you chose Beijing because your family has been living in Mongolia and hubby had been legally admitted for one year therefore meeting the requirements of choosing a different processing office than his home country. Him returning to Thailand doesn't change the fact that he met those requirements when you applied. The only part to be worried about if he returns to Thailand is if an interview is requested he must be able to travel to Beijing to attend. If that's not an issue, then you don't need to worry about the processing office.