I guess you mean that miners' incentive will become less and less overtime. Yeah, that might be true. If we assume that it will be globally adopted in the future and that its price will be less fluctuating, then each halving will simply make miners' profit halved, which means less computational power offered into the network and hence, less security.
It isn't that much of a concern. Miners cannot be concerned with fluctuating prices, so at the prices, we can estimate an electrical consumption of roughly 60Twh per year and that is excluding all the miners that are currently in the midst of being redeployed. Since fees in a block are quite variable, there is no point trying to estimate that. At current electrical consumption levels, the annualized consumption is more than Kuwait's which is quite significant. For each halving, which is every 4 years, for the sustained profits, we expect either a doubling of total transaction fees or price of Bitcoin just to maintain the profit margins.
Not out of the realm of possibility, 4 years is quite a long time. Even if we were to calculate using a far lower bound of computational power, it still wouldn't make sense or neither is it very feasible for anyone to attack it. The effects of halving is most significant at the start, with the transaction fees being more significant in the later parts.