Nothing has changed that would affect the answer since this question was originally asked in 2015.
As the question notes, the rules do not say if a ritual book can be replaced. They are mute on the loss and on the recovery of the ritual book. They do not say "if lost, the ritual book can never be recovered", nor do they say "if lost the ritual book can be recovered thusly."
TL:DR This is a question of rulings, not rules.
If the ritual book has been lost, it has been lost as part of the narrative of the game. If the book has been lost, the GM created a narrative in which the book was lost. The recovery of the book also needs to be part of the narrative. It is up to the GM to make a ruling that serves the game.
Can the ritual book from the Ritual Caster feat be replaced if lost/stolen/destroyed?
It is entirely reasonable for a GM to allow a ritual caster to replace a ritual book.
To not allow a ritual caster to replace the ritual book is to render the feat useless, which in most games is going to punish the player, probably for no reason, and is not going to lead to more fun.
How the book gets replaced will vary from campaign to campaign. Chances are, the difference in cost of 25gp for a blank book vs. 50gp for a spellbook is not significant. Furthermore, since wizards can write their spells on any old thing, it would not be completely unreasonable for a ritual caster to write rituals on something that does not necessarily resemble a conventional book. These are narrative issues that the GM and player should work out together.
More important than rules-lawyering from either the GM's or the player's standpoint is finding a solution that works and allow the game to move forward.
If replaced, does it contain any or all of the rituals in the old one?
Whether the replacement ritual book "comes with spells" can also reasonably vary from campaign to campaign. Even a maximally cooperative GM is unlikely to say, "In the back of the mysterious bookstore you find a new ritual book that has all your spells in it."
The GM can reasonably allow the ritual caster to acquire a new book and then have to spend time and energy replacing the spells; however, a smart GM will think about whether this narratively advances the game. Is replacing the rituals a challenge for the player to overcome? Have at it. Perhaps the ritual caster was imprisoned and has escaped. A stranger in a strange land they are without weapons, coins, or friends. Under the cover of darkness, they break into the old bookstore and find an empty book. Searching through the shelves, they find a familiar spell, find familiar. Things are looking up....
In other cases, the GM can reasonably handwave the whole thing.
Ritual caster: "Now that we're in Bigmagiccity, I try to replace my ritual book."
GM: "Yes, you have lots of connections in this town. Over the course of the next week, you're able to replace your book. Charge yourself what a book costs, and the cost to replace each spell."
For the GM, this isn't a rule, but a ruling. What is the best way to advance the story? It's completely reasonable in some cases that the details of replacing the book are not narratively important. A GM could even reasonably have a player roll, and on a good roll, recover more spells, and even maybe get an extra one, and on a bad roll perhaps they aren't able to find a replacement for floating disk. Again, it is up to the GM to make the rules serve the story.
Are either of the above dependent on the spellcasting class chosen when the feat was taken?
Not directly. The feat is not class-dependent. One class or another may have access to resources that make the story narratively different. A bard or a cleric would likely have access to different resources. If recovering the book is narratively significant then it is entirely reasonable that different classes would go about it in different ways.