I would NOT assume that your sister has "written you off" as someone put it, just because she didn't respond to your voice mails. She did respond to your e-mail. Bear in mind: People who have a gravely ill family member simply do not always have any time to make calls, update people, etc. It can be immensely painful for them to do so and to repeat to various relatives over and over the details. Your sister also may, like me, check her voice mail less and less if she uses e-mail frequently. So don't just say, "She wrote me off" because you have no idea what she has been going through in recent months or even recent years. She may have been in the difficult position of being a caretaker and having to watch her spouse die day by day. You don't know. Yes, she might have had your support if she'd been in closer touch. But how about taking the high road here and giving her the benefit of the doubt and assuming that she was in pain and profoundly busy?
Much of the post is about you and your brother. While that's sad, and painful for you, the BIL's death is not about you or your brother either. Go to the funeral only, skip any family gathering time afterward if you feel you must, but be sure that you get at least a moment face to face with your sister so you can tell her, "I was sorry to hear X was so ill, and I can only imagine how tough this has been for you. I know I live out of the area now but I have been thinking of you and that's why I'm here. I'll be in touch again to see how you're doing."
Then DO it -- get in touch. Use e-mail if she seems to respond better to that. If your brother tries to get into anything with you at the funeral itself, you need to be icy calm and just say, "Today is about Sister and BIL, not about us and our former issues. Let's just keep the focus on them." And do not, not, not respond or reply. If he comes drunk or aggressive to the funeral, yes, leave quietly.
If you do not go you may end up regretting it. Yeah, it could be drama -- but only if you LET it be drama. Don't try to socialize or pretend everything is lovely with the rest of the family. Focus on your sister and don't linger but be certain to have a moment with her. This is not about you or your brother or the estate. Say that to yourself over and over.
You sound very emotional in the post and that's understandable but you need to get some control over that. You can't break down or get into anything else during the funeral. The funeral service itself should mean you are all facing a minister or listening to speakers or whatever - not talking and interacting; so go, and get through the service.
You might even find your brother has gotten a slap of mortality thanks to his BIL's death and is more willing to be cordial than you realize. But you will never, never know if you don't attend. Go with your better instincts and attend, rather than assuming the worst. If it all blows up? Then you know you made an effort even if brother loses it on you.
One other thing --you could always just ask sister if you can attend.