In scripture as well as in the Didache, the only form it is found is in the Greek μαραναθά; the Aramaic form is believed to either be maran atha 'Our Lord has come' or marana 'tha 'O our Lord, come thou'.
So while I'm no expert in Aramaic, it would seem from what I read in the OED that assuming the form you suggested maran would translate as 'Our Lord' and atha would translate the English Perfect 'has come'.
In Semitic, the perfect is often used in prayer (ideally, God has already determined).
The same mentality comes in the DL of Chrystom when the Great Canon states "Remembering, therefore, this salutary command, and all that was done in our behalf: the cross, the tomb, the resurrection on the third day, the ascension into heaven the sitting at the right hand,
the second and glorious coming" it remembers things that have not happened yet..
