Her assets are also your assets. If she wants a divorce you cannot stop her. The court will endeavor to split your assets and liabilities on a 50%-50% basis. You may be entitled to maintenance. That is completely up to the court. I urge you to hire a local attorney and begin preparations. Good luck.
Separation and divorce are difficult on individuals if the parties are being reasonable and civil. When they are not, it is all the more stressful and confusing between all the legal and the emotional issues. You ask a number of good questions which can not be answered in a short simple way. You should definitely consult with an attorney to go into more specific details about your rights and protecting yourself. While you can not prevent her from obtaining a divorce if she is set on it, you can and should make sure you are protected and end up with a fair and just result.
As noted by others, these questions warrant a much fuller discussion in person with an attorney. Right now, your rights most likely will be to 50% of everything. If in the it appears in the future she will continue to make more than you and you will continue to make what you do now, there is likely an argument for her to pay you alimony, given the length of the marriage. For now, I do not want to speculate that you can get alimony or not, but I would simply suggest it is on the table. Most attorneys will give you a free consultation, so I'd suggest visiting them very soon.
Each court approaches maintenance in its own way. There is no statute or standard.
BUT... MacDavis has software that judge's tend to use.
It determines NET (after tax income for both parties), then it subtracts the smaller from the larger and divides it in half. The court will then determine reasonable expenses of the less income and determine if their income will support those expenses. If there is need, then maintenance may be ordered up to that need. The period is generally 1/3 to 1/2 the length of the marriage, but 25 years would be considered longter and may be substantially longer.
You definately need an attorney to protect your maintenance rights.