In my opinion there was nothing TSMC could have done. Altera left TSMC because of Xilinx. Xilinx is a fierce competitor on all fronts: financial, marketing, sales, technology, ecosystem, etc… so there is no way Altera can outrun Xilinx on a level playing field. TSMC is open to all customers and does not do exclusive partnerships so Intel was a smart choice for Altera.
The question is: Can Intel be a good foundry partner for Altera? My guess is yes they can, as long as the new Intel CEO is on board with it and Altera does not need ARM (ARM and Intel do NOT mix). Not great news for Intel’s other FPGA partners though (Achronix and Tabula). They must really be steaming over the "exclusive" Altera deal!