Apologies if this isn't the right place for this, but I would gladly accept any help in redirecting if not. I had originally booked a Star Alliance award trip for this summer via ANA, including a JTR-MUC-ORD leg to return home. The JTR-MUC flight has been canceled and after a confusing call to ANA where I reiterated multiple times that I did not accept the change and just wanted to understand my options, my itinerary now shows just MUC-ORD (where before it still contained the JTR-MUC flight first with an alert that there was a problem with that leg). Now I'm left with two questions:

1. Since the flight to connect me to MUC no longer exists, is it possible for them to start my return journey in a different location (such as ATH as that's easy to get to)?

2. If not, if I were to book my own flight to MUC and connect with my itinerary as it currently exists, how much trouble might I face having separate tickets on separate carriers ATH-MUC and MUC-ORD? This would be a roughly 6-hour connection where I'm not planning to leave the airport, and I'm mostly concerned with immigration/boarding issues, but I do understand the normal connection/delay issues that can come from having separate tickets.