What happens if the second reviewer for a conference proceeding keeps missing their deadline? I have submitted a journal article to a conference proceeding which will be held in June this year. Though I submitted it on time in December and the first reviewer accepted it in the first week itself, still I didn't receive a second reviewer's response. In the online submission system it appears as initial submission status, with the phrase "reviewer missed the deadline" repeated thrice in red color. If I cannot get a second guest editor what will happen to the article? Is it possible to accept an article without a second editor? How long would this usually take?
This is not your problem but the conference organizer's one. They have to ensure a proper reviewing process. 

Usually, they are contacting the reviewer and apply some pressure. It they still get no review, they acquire a third reviewer as replacement (or a program committee member does it by themselfes).