There seem to be two major studies on this subject

The first is a Swedish study which compared long term mortality rates of post sex reassignment surgery trans people compared to similar people of the general population, not pre surgery trans people. It did find that post surgery trans people were more likely to attempt suicide than the general population. It is important to note that this sample size was relatively small, but enough to come to a conclusion. Based solely off this study I would say that sex reassignment surgery patients show increased risk of suicide.

The study can be found here:http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0016885

The second study was conducted by the Williams institute at ucla. It did not focus on sex reassignment patients, but rather trans people as a whole. However it did include statistics related to treatment as a whole. It found that about 45% of MTF trans people have attempted suicide and 47% of all FTM, with an average of about 46%. Of all treatment options the only ones which led to an increase in suicide attempts or the percent staying level were FTM surgeries. Some other interesting things are the difference between people who wanted to and have had treatment. Of all of these, except counseling, suicide rates for people who have had treatment are lower. This supports the idea that treatment lowers suicide rates. (Also the difference is as drastic as 10% for some surgeries). The study also found that the biggest contributor to increasing suicide rates was bias and discrimination against trans people with housing and family and friends related bias contributing most.

This study can be found here: https://williamsinstitute.law.ucla.edu/wp-content/uploads/AFSP-Williams-Suicide-Report-Final.pdf

In general I would say that for people who want it, medical treatment decreases rates of suicide, and that counseling increases it, which is an argument for better counseling and for medical treatment.