'Dead' is a strong word. The times have always been changing. The younger generation has always been thought of as lazy by the older generation, and the older generation has always been blamed for the problems the younger generation is facing. There's a lot of hype and hyperbole used to sell ideas, and it works, in part, because feelings seem to win over facts, most of the time, and generational/institutional knowledge seems to go the way of Lessons Learned - it gets stored somewhere and forgotten.
It's been true, for while, that big bang approaches aren't always the best way to go. It's kind of like crime statistics and the media - people felt safer when the main crimes they knew about were the crimes in their own neighborhood. Now, people have access to information on global crime rates, and some crimes are given a lot more attention than others, blowing them out of proportion in order to drive an agenda. It's also kind of like car seat companies lobbying for laws that require kids to be in car seats until they reach a specific age, weight, and/or height. Who is really benefiting from the change?
All that being said, YES, companies do need to look at their objectives and determine the best way to accomplish them, whether that be big bang or incrementally/iteratively adding value. It's almost always better to add value quickly, but quickly is a relative term, and sometimes the quick wins aren't where your time is best spent. And who says a monolithic program can't change? It should adapt to a changing environment, but that doesn't mean the program failed or should end.
Does the role of the project manager need to change? Generally speaking of project managers as a group, no. Individually, if a project manager is locked into one way of doing things, then yes, absolutely, regardless of what that one way is. In 16 years as a project manager, I've heard of command and control projects, but never been on one. My role has always involved adapting to circumstances, culture, etc... We were doing iterative work and breaking large projects into smaller pieces before we knew Scrum existed or had heard of Agile. Project Managers need to understand the nature of the work to be done and the culture of the people they are working with in order to be successful. This doesn't change.
How does the PMO need to change? Which type of PMO are you talking about? There are companies where the PMO plays a consultative role, has influence with the decision-makers, and is able to quickly adapt to changing times. This is great, but the PMO can't make this happen on its own. In most companies, the leadership culture needs to change and be adaptable for the PMO to play a stronger role.
Does the approach to portfolio management need to adjust? Probably. When you consider that a lot of companies either aren't doing it, or aren't doing it well, there is a lot of room for improvement.
It's easy to speak of these things as needing to be a certain way, in a PMI-related forum, but a lot of companies don't see the connections between project, program, and portfolio management the same way PMI presents it. There are still companies that don't know the difference between a PM and a BA.
Times are changing, and some companies need to change more than others, but a lot more change is needed before big bang approaches will never be needed again, if at all. Consider building a space shuttle. You can build the parts incrementally and develop the software iteratively, but you can't launch it, or realize value from all of the work, until everything is done. I used to work in corporate events. We could break up all the planning and preparation into smaller pieces, but it all came together in one big bang.
The software world is evolving to where even large ERP systems are becoming less reliant on big bang approaches, but there's still a little bit of a cycle taking place between monolithic and distributed systems. Twenty years ago we had ASPs, today we have the Cloud. Maybe they're not exactly the same, but the saying that "Everything old is new again," doesn't just apply to fashion.