Is it mutar (l'chatchila, not shaas hadechak) to not go to minyan on yahrtzeit, and have someone say kaddish on your behalf? (Not to be lazy, but a valuable opportunity presents itself that would not allow you to make minyan?)
It is not mutar to miss a minyan lechatchila. However, if there is such a circumstance (such as being in a city with no minyan) then one can arrange for someone else to say kaddish.
Another reason for this to occur is to be in a minyan in which only one person says kaddish (rather than a group) and the individual involved cannot get a kaddish opportunity.