I'll give it a shot. Yes, your wall will eventually rot out. How soon depends on the quality of the installation. If drainage was properly provided to route water away from the wood as much as possible, it will last longer than if it wasn't. No way to tell how it was installed. If the timbers are pressure treated, as they most likely are, insect and moisture damage is slowed. Since the US is a big place, and prices for labor, and sometimes materials, can vary considerably from one place to another, the only way to know the cost of replacing it is to get a local contractor or three with good references and a reasonable amount of experience to come out and give you a quote.

It can probably be presumed that the lot grading for the subdivision is such that lots are all graded to drain independently out to the street on each individual property, so that creating a drainage problem for a neighbor is not likely, but then again, this lot could have slopes and drainage across lot lines, in which case interruption of flow is an issue. My understanding from another post by the OP on this same garden was that theot was flat, and the intent to build raised beds was more for aesthetics as well as making vegetable raised beds that would have improved soil conditions and be easier to work. The idea of a french drain as sketched out by the OP, which seemed to form a circle at the base of the proposed raised beds but didn't actually connect with anything, didn't seem to make much sense in terms of actually solving a drainage problem, in fact, if the lot is flat, they would seem to have been superfluous to solving the problem of a wet crawl space under the house, which sounds more like it was related to roof downspouts unconnected to drain lines to take it away from the house. I had originally understood the back of the lot to have the lot behind it at a higher grade with a slope beyond the proposed raised beds, but the sketches did not appear to support that line of supposition. In any case, I'd suggest that the OP either hire a competent landscape architect or designer/contractor to give him more informed advice on solving his problems and avoiding unnecessary expense or useless construction, or read up more to become better informed about landscape construction and particularly drainage concerns as they would pertain to his Fremont location. As it is, the questions have been too general to give truly informed advice, and not enough information has been supplied to really address all the potential concerns. I'd hope that these discussions have been sufficient to alert the OP that he needs to either hire some informed help, or get up to speed with the information needed to make the best decisions on how to proceed. There are definitely times when it saves money and expense to hire expertise...

It's difficult to predict the life span of your wall. A major unknown is how the fence upright supports are integrated into the wall and if they extend into the footer or below. If I understand your first post, the block cavities were originally filled with dirt. I have a hard time believing the contractor removed all that dirt and replaced it with concrete unless I saw him do it. I would probably dig down behind the wall and drill through the block to see what was in the cavities near the footer. With all the unkowns, here is my best guess. There is no steel tie from wall to footer and a major weakness is at this junction. The soil will exert a force against the wall that would over many years cause the wall to tip over. The fence will have an added force that at times will be in the same direction as that of the soil force and at other times the fence force will counter the soil force, but only in the area of the fence supports. The effect of the live load from the fence will cause hairline cracks between wall and footer beginning at the fence support and then elongating. The fluctuating forces will also lead to vertical cracks through the wall somewhere between the fence supports and the mid point between fence spans. When the cracking reaches a critical point the wall will begin to move. If the failure occurs in the spans between fence supports, it will likely be a slow failure. Failure at the fence supports in a wind storm where the wall blocks separate near the supports could be sudden. Expect the cracks. Watch for any shift or movement from vertical or any irregularity in the wall face. Be prepared to make repairs. One to two years for beginning cracks. Two to eight years to first wall movement.

You need a book; no one can give you advice on this without seeing, and even if they did it would be irresponsible to do so without knowing how you work. So grab the stone, as much as you can get - you can probably get rid of excess if you end up with it - then take your time reading and planning so you do the job right. Remember that stone can also be bought, probably the same kind or similar enough to blend in. So don't panic if you're a few stones short.