This was posted in another forum in a discussion about the same topic...
I discussed this situation in the confessional (FSSP priest) a few months ago. I actually was going to confession for something else, but thought I'd ask about me having missed going to Mass the previous Sunday, since I was out of town on a vacation. I told him that a TLM was not available.
He then asked if a regular Catholic church (or diocesan church - can't remember his exact words) in the town, and I said, yes, there probably was. He then said that unless it's a grave inconvenience, then I have to go to mass at the local Catholic church. He then said something about just sitting in the back of the church with my missal...something like that.
I didn't think to ask about whether or not it would be okay to not attend due to an irreverent Mass, but I suspect that his answer would still be the same.
He considered that it was a mortal sin for me to miss Mass, and gave me the appropriate penance as such. I guess I'll just have to consider it as a good test of character for me to have to go to an NO Mass when I go on vacation next.
Hmmm... When I went to confession at the SSPX, the priest told me the exact opposite. I told him that I had missed Mass for some time. He then inquired about my travel distance to a TLM, which I informed him that it was roughly 4.5 hours round trip. I then asked if I could attend the N.O. if nothing else was available. He told me that it would be a grave sin if I submitted myself to sacriligeous worship, and that I am not canonically bound to attend even the TLM due to my distance hardship, but he adviced me to make the sacrifice to try and make it once a month. So, I guess it matters what "brand" of Traditionalists priest you ask about this, but I firmly believe that my priest was absolutely correct on the matter.