Your STBX's lawyer has NO ability to "promise" anything in regards to you being in default! This is determined by the state's proscribed time limit for you to respond to the petition (usually 20 days). If you don't respond, you are in default. Your stbx may choose not to officially file for default, but it is highly unlikely to happen like that as it to HIS ADVANTAGE to file for default! It's the most common way of moving the case forward when the respondent in the case does NOT respond.
Also, you should have been officially served all the court papers already filed and signed some sort of acceptance or waiver of process server. If not, there's been some sort of miscarriage here... Either way, get a copy of the petition ASAP! Read it over very carefully. If there's anything you don't agree with, you need to file a response ASAP!! Otherwise, you will lose the opportunity to have a say in the process. Not repsonding essentially says you agree to what's in his petition.
Now, since you don't have kids with this guy and apparently don't own property together (if I remember correctly from previous posts), this really can be a simple divorce. Maybe letting it go to default will work, as it saves you the cost of responding. However, you once mentioned that you wanted support. I seriously doubt your stbx's lawyer would "recommend" that to his client, since you two weren't married for long... What's the deal, here, Akyavasha? Has that been addressed? And NOT just verbally, but in writing IN THE PETITION. If not, you will not get support, period. You are in over your head if you are following the advice of your stbx's lawyer. Remember, from an ethical standpoint, his lawyer SHOULD represent HIS client's interests--not yours. The only thing I can think of that would justify you not filing a response is if you are going to agree to everything he wants and then let it go to default OR file a consent decree. Are you two planning on signing a consent decree?
Just to recap, once the time limit expires, your stbx can file for default at any time. In fact, something MUST be filed within about 90 days (either default or consent decree), in order to keep the case active.
It sounds to me like you have let the time limit come and go, since you still do not even have a copy of the petition. Why weren't you served properly? Your MIL is NOT authorized to serve you, but it sounds like even that "process" did not yield a copy delivered to you. Didn't your JAG advisor mention anything about being properly served the court documents or responding in a timely manner?