Oh she could stay until she was well into her 40s if she really wanted to but she has mentioned that she wants to have kids and i can see that happening sometime in the next few yearsAn article was out today that all pros are back next year (though I saw something that hinted at Anton being a judge instead of pro). That means that Karen who is 39 in April will still be there so Dianne could do another 7-8 series.
All depends on whether or not she has other plans (like marriage, kids etc) and also on how her next few years on SCD go. Hopefully she gets a contender this year and has a good run which should hopefully keep her position safe for a while. Also someone who she clicks with - I don't think she and Max George really suited each other and were only paired up because of height reasons.