Miele refrigerators are often installed in higher-end kitchens, but the repair-vs-replace math should still prioritize risk and remaining life. With a conservative ~10-year expected lifespan for mainstream Refrigerators, it's usually reasonable to repair a newer unit for serviceable parts such as fans, defrost components, gaskets, and a single control module if the quote is below the threshold.
If the failure is compressor or refrigerant related, or if multiple electronic components are implicated, replacement becomes more attractive because costs can escalate and the chance of another major repair increases as the unit ages. Also consider downtime: refrigerator outages can lead to food loss, which effectively raises the "cost" of repeated failures.
The replacement price used is a representative mid-market French-door listing from a major retailer; Miele pricing can be higher depending on built-in configuration and capacity.