If the will is valid and yet all the assets were passed onto my sister, then the will won't help me because all of the assets now legally belong to her, right?
Essentially, yes. Legally, the provisions of a will only control the disposition of assets that are part of the probate estate. Assets of the deceased that are jointly owned with someone else and have right of survivorship or that have beneficiary designations are not part of the probate estate. Those assets legally pass to the surviving joint owner(s) and/or designated beneficiary immediately upon death.
There is a possibility that the joint ownership and beneficiary designations could be attacked on grounds such as the exercise of undue influence and possibly some other grounds. And that those assets could be brought into the probate process. But, it is a difficult (and likely expensive) argument to make and win. You would need an attorney with extensive knowledge of Texas case law and some pretty convincing evidence to prevail.
And since she IS for sure the executor then she has the right to get the insurance even though she's not the beneficiary?
No, she
is not the executor unless probate was opened and the probate court appointed her as executor. Merely nominating someone in the will to act as the executor does not give that person legal authority. Even if she had been appointed by the court as executor, she should not have been able to obtain the insurance proceeds if there were living primary and/or contingent beneficiaries on the policy. If she has obtained the proceeds, then:
1) She was named as the beneficiary on the policy (likely), or
2) She lied to the insurance company and the company did not require much evidence (unlikely).
And if she's not on the insurance as beneficiary then there is still a chance that the Will will work in my behalf but it has to go through probate for this to happen?
Yes, but, as I said, if she obtained the insurance proceeds, it is likely that she was the named beneficiary on the policy. The provisions of a will are only legally effective when the will is accepted as valid by the court and the assets that are subject to probate go through the probate process.