tiny dilemma on sewing machine

[shock-treatment.livejournal.com]

hello!
i was working on my bag...sewing a really LONG stitch, it took forever to pin in place & i started to stitch, i was more then halfway to the end & BAAAAM my bobbin runs out of thread.

so my question is...do i have to use the seam ripper to undo all the seams? or may i just begin stitching from where i left off & do a back stitch? or would that make my bag fall apart? would the seams be durable?

thanks! ♥