Bummer, don't let this get you down though. They say there are two kinds of riders, those who have been down and those who are going to go down. Yall have put on a LOT of miles, so do not be too frustrated with yourselves.
Would it be possible to have a bike sent to you from Canada? Then you could have your folks register it at home before it goes down there.
Also you will have to forgive me, but there are welders in every city, why not get the frame welded, fix the bike and continue onward? If you need a flight home then fly home for a week or two with the bike in storage and continue onwards. Or... I think you could always stick the bike on a ship and ship it across the gap to Colombia now. I know you would miss a few countries but the money saved from missing a couple countries would perhaps make up for some of the funds to fly home, or fix the bike etc.
Hey if you do decide to go back to Canada I am sure everyone you know will support your choice. (So long as you feel it is the right thing for the both of you. We just all know how much yall have said you enjoy the trip so far, and want to give you hope.)
Best wishes from our family and we will be praying for you both!